Omeisaurus (meaning "Omei lizard") is a genus of sauropod dinosaur from the Middle Jurassic Period (Bathonian-Callovian stage) of what is now China.

[4] The initial discovery of Omeisaurus was in 1936 when Charles Lewis Camp and Yang Zhongjian collected a partial skeleton from strata of the Shaximiao Formation in Sichuan, China.

[7] In 1955, Xuanmin Li and colleagues collected several Sauropod remains from the same strata as O. junghsiensis in Changshou during construction of a reservoir.

[7] During the construction of the Wujiaba Dam in Zigong during the mid-to-late 1970s, crews discovered many large Sauropod remains from strata of the Upper Shaximiao Formation.

[7] The amount of material was vast and was collected by the Chongqing Museum of Natural History over five years, and was prepped and briefly described.

[9] Interestingly, O. tianfuensis was discovered to have a tail club on the end of its caudal vertebrae based on a specimen from Dashanpu.

[13] O. maoianus was collected by Jin Xingshen and Zhang Guojin during the 1990s and the remains consisted of a skull, partial vertebral column, and several additional postcranial elements (ZNM N8510).

[13] O. maoianus' generic assessment has been questioned, with several phylogenetic analyses finding it more closely related to Mamenchisaurus and Xinjiangtitan.

[1] However, it and other Jurassic sauropods from Asia formerly assigned to Euhelopodidae are now placed in the separate family Mamenchisauridae, which is more basal in Sauropoda.