Xiaosaurus is a genus of dinosaur belonging to the family Hypsilophodontidae. It lived during the Middle Jurassic period, approximately 169 to 163 million years ago, in what is now China. The first fossils of Xiaosaurus were discovered in the early 1980s. During excavations near Dashanpu in Sichuan in 1979 and 1980, two specimens of a small herbivorous dinosaur were discovered.

Xiaosaurus, a member of the ornithischian group, was a relatively small dinosaur, measuring around 1 to 2 meters in length. What made it unique among dinosaur lineages was its distinctive hip structure. Like other ornithischians, Xiaosaurus was an herbivorous dinosaur equipped with a beak-like mouth, which was well-suited for cropping and grinding vegetation. It is believed to have possessed numerous teeth that efficiently processed plant material.

Given the limited fossil evidence available, much of Xiaosaurus' behavior remains speculative. Its small size and bipedal locomotion suggest it was likely an agile and swift runner, which may have aided its survival and evasion of predators. Like other ornithischians, Xiaosaurus may have lived in social groups or herds, offering protection and facilitating interactions for mating and resource utilization.