Abstract: Recently, a large number of dinosaur fossils were found in the Middle Jurassic Xintiangou Formation in Xinjin Township, Yunyang County, Chongqing, and the dinosaur fossils were intermixed with fishes, turtles, plesiosaurs and bivalves.This is the first discovery in the Xintiangou Formation.The Xintiangou Formation in the study area is preliminarily determined to be a littoral-shallow lake subfacies and partly a flood-pan subfacies, as shown by field measured section, rock features, sedimentary structure, paleontological features and grain size characteristics.The discovery of the fossil assemblage of Xintiangou Formation in Chongqing area provides more evidence for the study of Mesozoic fossil and paleoenvironment in the Sichuan basin.