The origin and evolution of mammals must be controlled and constrained by their living environments,so the characteristics and variations of their fossil species and assemblages are one of important signals reflecting the climatic and environmental changes. The East Asian mammalian faunas underwent several significant turnovers during the Late Cenozoic. There was a dramatic turnover event of mammalian faunas in the transition between the Middle and Late Miocene, namely, the forest-adapted Platybelodon fauna was replaced by the grassland-adapted Hipparion fauna. The global climatic change peaked in the Middle Miocene with the marked reducing of Antarctic continental ice-sheets and the further rising of ocean bottom temperatures, so that the Middle Miocene Climatic Optimum (MMCO) was formed from 17Ma to 15Ma, representing a major warming event irrelative to human activities in the geological time. The Middle Miocene mammalian faunas in China had sensitive responses to the MMCO warming event, so a large number of warm- and wet-adapted mammals appeared, such as Platybelodon, Pliopithecus, beavers, dormice, Anchitherium, Chalicotherium, Kubanochoerus,listriodonts, and Palaeotragus. The Middle Miocene Platybelodon fauna reflected relatively warm and wet climate and environment, and Pliopethecus and other typical forest animals dispersed even into Xinjiang, Gansu, Ningxia, and Inner Mongolia of North China under this background. Although almost all of the Chinese Middle Miocene mammalian faunas are preserved in fluvial and lacustrine deposits, especially fluvial sandstones, lacking dense fossils concentrations, there are sufficient materials to show the adaptive characteristics of mammals to warm and wet environments,thus there are enough records to display the behavior and response of mammals during the MMCO.