Yimenosaurus, which means "Yiman Lizard," is a genus of sauropodomorph dinosaur from the Early Jurassic period in China. This genus was formally established in 1990 by Ziqi Bai, Jie Yang, and Guohui Wang. It includes its type and sole species, Yimenosaurus youngi, named in honor of the renowned Chinese paleontologist Yang Zhongjian, also known as C.C. Young in English. The known fossils of Yimenosaurus comprise the holotype, which consists of an almost complete skull and mandible, along with incomplete cervical and dorsal vertebrae, a mostly complete sacrum, ilium, ischia, partial ribs, a complete femur, and a paratype represented by well-preserved postcranial elements and a partially preserved skull. Its length is estimated to be approximately 9 meters (30 feet) and its weight to be around 2 tonnes (2.2 short tons).

Yimenosaurus is a well-known sauropodomorph dinosaur due to the abundance of fossils from multiple individuals attributed to this genus. Yimenosaurus is recognized for its substantial size, with some estimates suggesting it may have exceeded nine meters in length, hinting at the possibility of an even larger size. This places Yimenosaurus among the largest sauropodomorph dinosaurs discovered thus far.

During the Early Jurassic period, Yimenosaurus inhabited China. It is noteworthy that even at this early stage, the characteristic quadrupedal body form, which later sauropod dinosaurs descended from sauropodomorphs would adopt, was already becoming apparent.