||During the past several decades, the paleoecology of the Mammuthus-Coelodonta Faunal Complex in the Palearctic has been thoroughly explored, especially using stable isotope analysis. Numerous studies have documented high ecological plasticity and regional heterogeneities for this fauna. However, very limited attention has focused on Northeast Asia, at the southeastern edge of the distribution of the mammoth steppe biome. In the present study, we undertook radiocarbon dating, zooarchaeology by mass spectrometry (ZooMS), and stable isotope analysis on the fossil faunas from Yanjiagang Paleolithic site, Northeast (NE) China, and from the Geographical Society Cave in the nearby Russian Far East, to explore the paleoecology of this fauna in this middle-latitude region. Isotopic (δ13C, δ15N) data from these two sites suggested that the woolly mammoth (Mammuthus primigenius) was a grazer feeding on grasses/sedges, while the woolly rhinoceros (Coelodonta antiquitatis) and steppe bison (Bison priscus) utilized a wider range of food resources. All megaherbivores exhibited some ecological plasticity. Meanwhile, the mammal remains from Geographical Society Cave prevalently exhibited lower δ15N values than those from China, indicating variable environments and vegetation in Northeast Asia during MIS 3. Interestingly, through reevaluating the diachronic mammal distribution and ecology based on direct radiocarbon dating and ZooMS, we report the credible presence of Bubalus, typically interpreted as a mild climate faunal element in the Pleistocene, within the Mammuthus-Coelodonta Faunal Complex in Yanjiagang. This emphasizes the unique scenario of this biome in Northeast Asia, where the fauna exhibited sensitivity to synergic effects of climatic oscillations and local geographic traits. After comparing isotopic data of mammoth from different subregions of Asia, we found that NE China displayed both highest δ13C and δ15N values, possibly related to the higher temperature compared to the Arctic regions. This study reveals the characteristics and complexity at the southeastern limit of the range of the mammoth steppe biome and urges more systematic studies within and outside this region.