Rubeosaurus is a genus of ceratopsian dinosaur from the Two Medicine Formation of the Upper Cretaceous Period (75 to 74 million years ago). It lived in what is now North American and its fossils were discovered in Montana. The type species is R. ovatus.
This species was formerly assigned to Styracosaurus, and juvenile specimens that were incorrectly referred to as Brachyceratops, may be juvenile Rubeosaurus.
It is notable for its large broad-based nasal horn and the ornamentation of its bony frill. There were one or two pairs of straight spikes on the edge, with the two spikes closest to the midline pointing so that they converged (touched or joined each other).