"Ceratosaurus" was a medium-sized theropod. The original specimen is estimated to be or long, while the specimen described as "C. dentisulcatus" was larger, at around long. "Ceratosaurus" was characterized by deep jaws that supported proportionally very long, blade-like teeth, a prominent, ridge-like horn on the midline of the snout, and a pair of horns over the eyes. The forelimbs were very short, but remained fully functional; the hand had four fingers. The tail was deep from top to bottom. A row of small osteoderms (skin bones) was present down the middle of the neck, back, and tail. Additional osteoderms were present at unknown positions on the animal's body.