The discovery, first of its kind in Xinjiang, was made earlier this month by researchers with the Institute of Archaeology of the Chinese Academy of Social Sciences in Qagan Gol Township, Qinghe County.
Scattered bones were found in the large casket, which is about 3 meter long and 1.65 meter wide.
Associate researcher Guo Wu, who led the excavation, speculated that the casket was not the first home of the remains, but noted that conclusion could only be confirmed after scientific tests.
The large coffin was built between 3,800 and 3,500 years ago and small one between 2,800 and 2,500 years ago.
The researchers speculated the small casket was made by those who wanted to "reuse" the large one, state-run Xinhua news agency reported.
Guo said they are using a drone to obtain images of the coffins from all angles, adding that the findings are significant for research on the history and culture of early nomads in the Altai region.