It first appeared as an Abra in IL022: Abra and the Psychic Showdown. It first appeared as if it was sleeping. Sabrina used Kadabra in a Gym Battle against Ash's Pikachu. Whilst the two Pokémon battled, Abra evolved into Kadabra. It displayed great strength after it's evolution by controlling Pikachu's Thunder with Confusion turning the attack not only against him but into what appeared to be a dragon made of electricity. It used Psychic to slam Pikachu on the ceiling and on the floor repeatedly until Ash couldn't take it and forefited the match causing it to stop the brutal onslaught.
It later appeared in IL024: Haunter Versus Kadabra. It was supposed to battle Ash's Haunter but it was nowhere to be seen. Later, in Ash's re-rematch Kadabra battled Pikachu again and was tougher than before, especially with attacks like Teleport and Psybeam. Just as Ash thought he had the battle won with a devastating Thunder attack, Sabrina told it to use Recover and all the damage it took was gone. When Sabrina was laughing because of Ash's Haunter's slapstick, Kadabra was laughing as well since they were both psychically linked, making it unable to battle.
Kadabra is the first Pokémon to evolve during a Gym battle with Ash.