Abstract: Niuyan Cave is located at Niushou Mountain in Mentougou, Beijing（39°54' N latitude 115°36'E longitude). A 1ot of vertebrate fossils were excavated from this cave, including many mammalian skulls and limb bones as well a few bones of birds. The mammalian fossils are recognized as Panthera pardus, Ovis nahoor and Pseudois nayaur．Specimens of P. pardus from Niuyan Cave are smaller than all the other known fossil records, e. g. P. pardus from Zhoukoudian and Gongwangling. They are also smaller than most of the recent P. pardus. Recent P. pardus disfributes in many regions of Asia and Africa. The body sizes of recent P. pardus reflect the Bergmann's Law typically. The more their distribution regions are close to the tropics, the smaller their body sizes are. The smallest subspecies of recent P. pardus is P. p. nanopardus that distributes in Somalia near the equator. The Yinxu fauna from Anyang and the Upper Cave fauna during the warm period contained the minor P. pardus, but P. pardus from Niuyan Cave is even smaller than them. According to the Bergmann's Law, the small P. pardus from Niuyang cave shows that it should live in hot south regions and be a tropical or subtropical animal. The discovery of the small P. pardus fossils from Niuyan Cave indicates that the climate in Beijing district at that time was very warm. Combining with the stratigraphic distribution of Ovis nahoor and Pseudois nayaur, the age of these mammalian fossils should be of late Late Pleistocene, about 30ka— 20kaB. P. There is no any human trace in Niuyan Cave. It might be a natural trap for animals.