Pikachu is a short, chubby, rodent-like Pokémon with yellow fur all over its body. Pikachu's ears are long and come to a point with black tips. It has a small mouth which resembles a sideways 3, it has black eyes and two red circles on its cheeks. Its forearms are short and somewhat stubby, with 5 digits on each "hand" and its feet have three digits. It has two brown stripes on its back, and its tail is in the shape of Zigzag-styled lightning bolt, with a patch of brown fur at the base of the tail. It's technically a quadruped, but has been shown to be able to walk upright on its hind legs.

Besides its evolution and pre-evolution, it may be related to Plusle, Minun, Pachirisu, Emolga and the Marill evolutionary family due to their many physical similarities.