Rhyhorn is a rhinoceros-like Pokémon with a body covered in gray, rocky plates. Its underside and rear are smooth, and it has four short legs with two claws on each foot. It has a triangular head with narrow, red eyes, two fangs protruding from its upper jaw, small, triangular openings on the upper sides, and a horn on the tip of its snout. A female will have a shorter horn than a male. A spiked ridge runs along its back. In addition to its rocky hide, its bones are a thousand times harder than human bones.

Rhyhorn's brain is very small, giving it a one-track mind. When it runs, it forgets why it started and continues until it falls asleep. However, it may recall the reason for demolishing something. Due to its short legs, it is inept at turning and can only run in straight lines. It does not care if obstacles get in the way, merely smashing through them or sending them flying, although it may feel pain the day after a collision. This personality is how Rhyhorn expands its territory. Rhyhorn is powerful enough to shatter skyscrapers or mountains instantly after charging forward with head tackles. Rhyhorn lives in rough terrain. A Rhyhorn's territory expands to six miles.