Yunnanosaurus (/juːˌnænoʊˈsɔːrəs/ yoo-NAN-oh-SOR-əs) is an extinct genus of sauropodomorph dinosaur that lived approximately 199 to 183 million years ago in what is now the Yunnan Province, in China, for which it was named.

Yang Zhongjian (also known as C. C. Young) discovered the first Yunnanosaurus skeletons in the upper Zhangjiawa Member of the Lufeng Formation of Yunnan, China, dating to the Sinemurian stage of the Early Jurassic.

The holotype specimen CXMVZA 185 was collected in 2000 in terrestrial sediments deposited during the Pliensbachian stage of the Early Jurassic period, approximately 191 to 183 million years ago.

[4] However, scientists do not consider Yunnanosaurus to be especially close to the sauropods in phylogeny because the remaining portions of the animal's body are distinctly "prosauropod" in design.

Yunnanosaurus had been assigned to several taxa over the years, including Thecodontosauridae and Plateosauridae, but a more recent phylogenetic analysis conducted by Novas et al. (2011) shows that this genus is part of the taxon Massopoda in a clade with Anchisaurus and Jingshanosaurus.

The Y. huangi holotype specimen IVPP V20 and the Y. robustus holotype specimen IVPP V93, were collected by Chung Chien Young in terrestrial sediments from the upper dark/deep red beds of the Zhangjiawa Member of this formation, that are believed to have been deposited during the Sinemurian stage of the Jurassic period, approximately 199 to 190 million years ago.

Chung Chien Young had also explored the lower dark/dull purple beds of the Shawan Member of the Lufeng Formation and found more specimens that he later assigned to Y. huangi.

Specimen IVPP V32 was collected by Young in 1938 in dark red, argillaceous sandstone that is believed to have been deposited during the Hettangian stage of the Jurassic period, approximately 201 to 199 million years ago.