Bulbasaur first appearance was in Bulbasaur and the Hidden Village. When Misty tried to capture a wild Oddish, Bulbasaur rushed to Oddish's aid, easily defeating both her Starmie with Tackle and Ash's Butterfree by blowing his own Sleep Powder back onto him.
Later, the group met Melanie, who cared for sick, injured, and abandoned Pokémon in the Hidden Village. She revealed that she had raised Bulbasaur, that it acted as the village's bodyguard, and was blatantly hostile to all Trainers.
Later, Team Rocket attacked the village and attempted to steal all of the Pokémon with an enormous vacuum. Bulbasaur managed to save Oddish at the last second, and was touched when Ash dashed out to help him get to safety. It then used Vine Whip to deflect the vacuum and Pidgeotto drove Team Rocket away. After Team Rocket's defeat, Melanie encouraged Bulbasaur to join Ash, explaining that its growth was being stunted by staying too long in the village. Bulbasaur agreed to join him once Ash defeated it in battle. Bulbasaur put up an excellent fight against Pikachu, using its vines to seize and smash Pikachu onto the ground repeatedly. However, a powerful Thunderbolt fried Bulbasaur and stunned it long enough for Ash to capture it.
Bulbasaur was first used in a battle to repel Team Rocket Grunts aboard the St. Anne in Battle Aboard the St. Anne, where it joined a group of other Bulbasaur to use Vine Whip on the Grunts. Its vines were also used to help the gang and Team Rocket escape from the sinking ship in the next episode.
In Tentacool & Tentacruel, Butterfree carried Bulbasaur into battle with the giant Tentacruel, but it was easily swatted aside by a giant tentacle.
Bulbasaur's Gym battle debut occurred in Pokémon Scent-sation!, where it fought Erika's Tangela. It attempted to use Vine Whip, but Tangela used Constrict to pull it in close and defeated it with Stun Spore.
In The Ninja Poké-Showdown, Bulbasaur was used to battle Koga's sister, Aya, and her Venonat. After dodging Bulbasaur's Tackle, Venonat fired its Stun Spore. Bulbasaur, however, countered by blowing away the Stun Spore and used Vine Whip. Venonat was able to dodge Bulbasaur's vines and hit bulbasaur with a super-effective Psybeam. Bulbasaur, however, was able to endure the hit and after dodging another Psybeam it defeat Venonat with Leech Seed.
In Ditto's Mysterious Mansion, Bulbasaur was called out by Ash to battle Duplica's Ditto. Ditto immediately transformed into Bulbasaur and blocked an incoming Razor Leaf with Vine Whip. It then used Vine Whip to enwrap Bulbasaur. Unable to do anything, Ash forfeited the match.
In Who Gets To Keep Togepi?, Ash used Bulbasaur in the tournament to decide who got to keep Togepi. It faced Misty's unintentional entrant Psyduck and easily defeated the Duck Pokémon by licking and tickling it. However, the win meant nothing as Togepi chose Misty as its Trainer anyway.
Ash's Bulbasaur resisting evolution
Bulbasaur had the opportunity to evolve in Bulbasaur's Mysterious Garden. Bulbasaur was used in a battle against a Hiker's Rhyhorn. While Rhyhorn headed forwards using Take Down, Bulbasaur tried stopping it with Leech Seed. Bulbasaur, however, failed to do so and was hit hard. Ash tried recalling Bulbasaur, but it refused to return to its Poké Ball, wanting to continue the battle. As Rhyhorn charged in for another attack, Bulbasaur struck it with Razor Leaf and followed up with Vine Whip, knocking it out. Ash then noticed Bulbasaur had collapsed and that its bulb had started glowing and immediately rushed to the Pokémon Center. At the Pokémon Center, Nurse Joy revealed Bulbasaur was almost ready to evolve and that the evolution takes place at a special festival in the Mysterious Garden. That night, Pikachu noticed Bulbasaur leaving the Pokémon Center and the two had a conversation. Suddenly, Bulbasaur was grabbed by multiple vines belonging to a group of Bulbasaur and was taken away. While Pikachu went to get the others, Bulbasaur was taken to the Mysterious Garden where the evolutionary festival was about to take place. While all other Bulbasaur evolved into Ivysaur, Ash's Bulbasaur refused to do so, despite facing the mass of Ivysaur as well as a Venusaur, who were angry at it for ruining the festival. Ash then intervened and stood up for Bulbasaur and its decision not to evolve. Then Team Rocket appeared and used a vacuum to try to capture all Ivysaur and Venusaur. Since Bulbasaur didn't evolve, it was able to learn Solar Beam and used its new move to free the Ivysaur and blasted Team Rocket off. Venusaur then approached Bulbasaur and extended a vine to it as a gesture of respect. Bulbasaur, Ash and the others then left the garden, having made amends with the Ivysaur and Venusaur.
In Princess vs Princess, Bulbasaur, along with Pikachu and Brock's Vulpix, was briefly lent to Misty to allow her to compete in the Queen of the Princess Festival contest with a more balanced team. In the first round of the tournament, Bulbasaur single-handedly defeated a Trainer's Kingler, Pinsir, Cubone and Raticate. Later, it was also seen defeating a Graveler. Bulbasaur was called out again in the finals to battle Jessie's Lickitung. Bulbasaur tried attacking with Vine Whip, but its vines were tied by Lickitung's huge tongue got and licked, causing it to faint.
In Battle for the Badge!, Bulbasaur was sent out to fight Team Rocket, who were fighting in Giovanni's stead in the Viridian Gym. It faced Giovanni's Kingler. Despite the type-advantage, Bulbasaur was hit hard by Kingler, who blocked Vine Whip with Harden and then hit back with Bubble.
In Mewtwo Strikes Back, Bulbasaur was used to battle Raymond's Donphan. It was hit by two successive Rollouts, but when launched into the air, it was able to flatten Donphan with Solar Beam. On New Island, Bulbasaur and Squirtle attempted to resist capture by Mewtwo, using its vines to keep the Balls at bay. Ash recalled both Pokémon to safety, but both were cloned when Bulbasaur's Ball was captured itself. Bulbasaur fought viciously against its clone, but was the underdog, its clone able to headbutt it over and over. It wept when Ash was petrified by Mewtwo and Mew, its tears helping in his restoration.
It had only one battle in the Indigo League, in The Fourth Round Rumble against Jeanette Fisher. After an initial trouble with Beedrill's speed, Bulbasaur crippled the Poison Bee Pokémon with Leech Seed and then defeating it with Tackle. Scyther's speed and Double Team produces similar trouble for Ash, until Bulbasaur uses Vine Whip to hit every single clone until it knocks out the real Scyther. Looking set to sweep the match with just Bulbasaur, Ash then took on her Bellsprout. Bulbasaur used Tackle, but Bellsprout flexed its body and absorbed the blow, before seizing Bulbasaur and slamming it onto the ground until it fainted.
Its bond with Ash's Pikachu was shown for real in A Friend in Deed, where Pikachu was able to detect Bulbasaur's Poké Ball among hundreds of stolen Balls.
In Friend and Foe Alike it used its Vine Whip to help Ash escape from Team Rocket. However, it was not used for the fifth round because it had a type disadvantage against Zippo, Ritchie's Charmander.
It accompanied Ash to the Orange Islands and was used in Ash's second Gym challenge against Danny in Navel Maneuvers. It attempted to help Pikachu carve a frozen geyser into an ice sled, but was unable to keep up with Danny's team until Charizard completed it in a few short Flamethrowers. It then helped Ash, Pikachu and Squirtle in the race down the cliff, using its vines to steer.
In The Mystery Menace, Bulbasaur was kidnapped by a giant vined creature in the sewers of Trovitopolis. Ash was so upset by this that Misty and Tracey had to both physically restrain him from diving into the water after it and then tie him up so that Officer Jenny could rescue them. Ash kicked and screamed the entire time. With help from Muk, he rescued Bulbasaur and its captor, a mutated giant Bulbasaur that had been abandoned by the town's mayor.
In Misty Meets Her Match, Bulbasaur is used in the Grass-type round of the Gym battle for the Spike Shell Badge. It fought against Rudy's Exeggutor, who dodged Razor Leaf and knocked Bulbasaur down with Egg Bomb. Bulbasaur quickly saved the battle by putting Exeggutor to sleep with Sleep Powder. Bulbasaur was on Ash's team to fight Drake for the Orange League championship in Enter the Dragonite. It managed to land a few blows on Drake's Electabuzz, but was defeated by a ThunderPunch. Drake was eventually defeated and Bulbasaur joined the rest of the team in the Hall of Fame.
Bulbasaur joined Ash in Johto, where it first met Heracross in A Sappy Ending. This began the recurring joke of Heracross wanting to suck the pollen from Bulbasaur's bulb. Throughout the Johto journeys, Bulbasaur's oldest team members Charizard and Squirtle both went into training with others, leaving Bulbasaur as Ash's only remaining Kanto starter. In The Chikorita Rescue, Bulbasaur was used to battle against a Chikorita that Ash had interest in catching. It was recalled after being hurt by the small Grass-type Pokémon and was congratulated by Ash for its effort. Bulbasaur was used in Chikorita's Big Upset, where Ash ordered it to find Chikorita. It would again be irritated by Heracross, who after getting deployed by Ash against Team Rocket, wasted no time in trying to suck the pollen out of Bulbasaur's bulb. Bulbasaur scolded its teammate and hit Heracross with its vines.
It bid a solemn farewell to Squirtle in The Fire-ing Squad!. Bulbasaur fought for Ash against Misty for the second time in The Totodile Duel. It seemingly defeated Poliwag with a Razor Leaf, but Poliwag evolved into Poliwhirl and fought back with a powerful Body Slam. After taking damage from Bubble, Bulbasaur flattened Poliwhirl with Solar Beam, winning the match for Ash. It also had a rematch with Aya in Ariados, Amigos!, using Tackle to defeat Venonat from above. In The Grass Route, Bulbasaur was entered in the 45th annual Grass Tournament, reaching the finals after Team Rocket was disqualified for dressing Meowth up as a Sunflora. Bulbasaur looked set to win the final, but Ephraim's Skiploom learned Solar Beam and won the tournament.
Bulbasaur remained with Ash until Bulbasaur... the Ambassador!, when it was sent back to Professor Oak's lab to keep the Pokémon there from quarreling with each other. It proved to be a natural leader, first solving the territorial disputes between the warring Bellossom and Jumpluff factions, and the Grass-type and Water-type Pokémon by ordering and leading the construction of a new lake. It came very close to peril when it saved an Oddish from an enormous falling boulder, but revealed that it had learned Dig just in time to save itself. Oak remarked to Tracey that Bulbasaur was a perfect example of a Pokémon being able to call on powers unheard of in extreme situations. After resolving this dispute, Ash and Oak agreed to allow Bulbasaur to reside at Oak's lab for an indefinite period, finally rotating it out of his team.
It was called on in Tie One On!, where it fought in the Silver Conference against Jackson's Shiny Magneton. It quickly learned from Pikachu and Cyndaquil's mistakes, instead using a spinning Vine Whip to mow through the afterimages from Double Team. It blocked Magneton's attacks with Razor Leaf and Vine Whip, before taking it down with Leech Seed and Vine Whip. It then took on his Meganium, with whom it had a bitter rivalry after the Herb Pokémon had mocked it earlier. Neither Pokémon attempted to dodge the other's attacks, both willing to be able to take as much as the other. It came down to a battle of Vine Whips and a double Solar Beam, which knocked out both Pokémon.
Bulbasaur was seen in Showdown at the Oak Corral, and was one of the first Pokémon to realize there was something wrong. It later defeated Butch's Hitmontop and used a Solar Beam on the whole group.
In Hokey Poké Balls!, May showed her Bulbasaur to Professor Oak, which made Ash decide to bring his Bulbasaur over for a visit. When the Poké Ball arrived though, it wouldn't open, making everyone believe that the Pokémon Center's balls had been stolen. It was revealed to be Team Rocket, who accidentally dropped Ash's Bulbasaur while escaping. The two Bulbasaur teamed up to stop Team Rocket, with Ash's Bulbasaur teaching May's along the way. Once they found Team Rocket, the Bulbasaur battled against them, with Ash's Bulbasaur protecting and teaching May's how to fight. After rescuing the Pokémon, Professor Oak called back and asked for Ash's Bulbasaur to return and stop the Water and Grass Pokémon from fighting. Ash sent his Bulbasaur back to Professor Oak's Laboratory as May's Bulbasaur appeared to have made a positive change from the experience.
Bulbasaur later returned in The Right Place and the Right Mime, where May decided to leave her Bulbasaur at Professor Oak's so she could learn from Ash's Bulbasaur.
In Gathering the Gang of Four!, Ash brought it to his team alongside Charizard and Squirtle to battle Brandon at the Battle Pyramid. After Brandon's Dusclops took down Charizard, Ash's Bulbasaur was sent out to fight in the next episode. It took damage from the powerful Dusclops, including a Confuse Ray which sent the vines out of control and caused them to attack Bulbasaur and Ash. Bulbasaur responded to Ash's cries and broke out of confusion, leaping into the air and taking down Dusclops with Solar Beam. After Solrock took down Squirtle, Bulbasaur was sent back out. After taking damage from Psychic-type moves and responding with Razor Leaf and Vine Whip, a double Solar Beam knocked both Pokémon out. After Ash won, Bulbasaur returned to Professor Oak's Laboratory.
Bulbasaur made a cameo in An Old Family Blend! at Professor Oak's Laboratory, where Heracross was sucking sap from its bulb, much to Bulbasaur's annoyance. It used Vine Whip to shove Heracross away. Bulbasaur was not called upon for the Lily of the Valley Conference.
Bulbasaur appeared in a flashback in The Fires of a Red-Hot Reunion!.
Bulbasaur later appeared in The Dream Continues! at Professor Oak's corral, where it was being filmed by Alexa. It later had a happy reunion with Ash and Pikachu, before signalling to Ash's Unova Pokémon with its Solar Beam. It later posed with the rest of Ash's Pokémon in a group photo with him.