Abstract: A new sauropod, Tonganosaurus hei gen. et sp. nov. from the Yimen Formation(Lower Jurassic) of southern Sichuan, China, is described on the basis of a collection of bones. These fossils include about 20 vertebrae,a complete right pectoral girdle and right forelimb, the distal end of a left scapula,a pair of complete ischia,a complete right hindlimb, the proximal anddistal ends of a left femur, right metatarsals (mt.I, II, III and V),a right pedal ungual, and ten neural spine and rib fragments. The third cervical and anterior caudals are most similar in shape to those of the mamenchisaurid Omeisaurus(from the Middle Jurassic, Sichuan Basin), and quite different from those of other sauropods. The material was therefore assigned to the Family Mamenchisauridae Young & Chao,1972 and a new genus and species were established.This represents the first discovery of a sauropod in the Lower Jurassic of China since Gongxianosaurus was found in Sichuan Basin. The Tonganosaurus material is of great importance for understanding the phylogenetics of the early Sauropoda.