Abstract: A fragmentary juvenile mandible referable toGomphotherium wimani is described in this report. It was discovered at the Nanyucun Locality, Simen Township, wushan County, Tianshui area, gansu Province. Both the left and right p3, dp4, and m1 are completely preserved in this specimen. The cheek teeth show characters that are derived within the genus Gomphotherium, such as anteroposterior compression of lophids associated with wide interlophids, presence of weak posttrite central conules, multiplication of mesoconelets and central conules, and weak cementation. These features are consistent with the diagnosis of G. wimani. G. wimani was originally discovered in the Middle Miocene of gansu, and the fossiliferous horizon within the Nanyucun exposures that yielded G. wimani can be correlated with strata at neighboring Middle Miocene localities. Therefore, the G. wimanihorizon at Nanyucun should be dated to the Middle Miocene. In combination with palynological data, the discovery of G. wimani at the Nanyucun Locality implies that the paleoenvironment of the Tianshui area in the Middle Miocene was probably relatively warm and humid, suitable for large populations of brachyodont mammals such as gomphotheres.