Immunity prevents the Pokemon from being afflicted by poison.
A Pokemon with this Ability will be cured of poison if it is poisoned while in battle (such as if it gains the Ability outside of battle or by an effect like Skill Swap, or is poisoned by a Pokemon with an Ability like Mold Breaker). If the Pokemon is holding a Pecha Berry or a Lum Berry, it will be eaten before Immunity cures the Pokemon of poison.
Outside of battle
Pokemon with this Ability can’t take damage from poison outside of battle.
If a poisoned Pokemon gains Immunity by evolution or the Ability Capsule, it will not be cured of poison until sent into battle. Pokemon with Immunity will not be poisoned by the Gentleman’s Kirlia in the Battle Pike nor the Battle Arcade’s game board.
Pokemon with Immunity