The fossil is of an herbivorous sauropod dinosaur 115 feet in length and weighing an estimated 30 tons, researchers from the China Research Society of Paleontology said.
The fossil was found in Shanshan Country in a rock stratum of the Middle Jurassic Period about 165 million years old, Sun Ge, head of the expedition team and deputy executive director of the paleontology society, said.
The largest Jurassic dinosaur fossil discovered in China previously was less than 100 feet in length, the researchers said.
Paleontologists are performing an ongoing excavation of the fossil hoping to unearth a complete skeleton, Sun said, and have also unearthed a tooth fossil which apparently belonged to a carnivorous dinosaur not far from the herbivorous dinosaur fossil.
"We hope the future excavation will help unveil more evidence to suggest what caused the death of this mammoth creature," Sun told China's state-run Xinhua News Agency.
The expedition team has discovered more than 20 fossil sites in Shanshan, Xinhua reported.