Poison-type moves in Pokémon are strong against Grass- and Fairy-type Pokémon.

Offensive strengths

  • Poison-type attacks hit Grass-type Pokémon for super-effective damage, dealing 2× normal damage.
  • Since Generation 6 (X/Y), Poison also gained super-effective damage against Fairy-type Pokémon.

Extra context

  • Poison-type moves are resisted by Poison, Ground, Rock, and Ghost types, meaning they do reduced damage to those.
  • Poison-type attacks do not affect Steel-type Pokémon at all, so they deal no damage to them.

So if you are wondering “what is poison strong against” in Pokémon battles, the key answer is: Grass and Fairy types.