Whismur is a mauve, bipedal Pokémon with a spherical body. It has two stubby arms and two round, yellow-tipped feet that lack toes. Its ear covers are long and rabbit-like with yellow tips, and the ear openings can be seen as a hole at the base of each ear cover. Its eyes appear as cross or plus sign-like black marks, and it has a simple, wide mouth usually shown open. It has a small, plug-like tail with a hole in it and a yellow crescent marking above it.
Whismur's murmurs are barely audible, but when it senses danger, it lets out a cry at an ear-splitting level. While it is crying, it will cry louder from being startled by its own cries. It breathes through its ear canals, which allow it to cry continually without having to breathe. It stops crying when its ear covers are shut. It lives in caves.