During the second millennium bc, several significant changes were happening in prehistoric societies across Eurasia. For instance, shifts in subsistence practice occurred in north-western China, including the western Loess Plateau. However, the magnitude and nature of this dietary change are unclear and more detailed information and regional studies are needed in order to fully understand the reasons behind this change. In this study, palaeodiet is investigated at three sites (Xiahaishi, Buziping and Buzishan) in the western Loess Plateau, all dating to c.2000 cal bc, through stable isotope analysis of human and faunal remains, in order to explore the socio-economic conditions prior to the subsistence shift. In general, humans and omnivores (Canis and Sus) had diets dominated by millet. Compared to other sites in Gansu Province, the humans and omnivores in this study were more reliant upon millet-based agriculture, and millet-based agriculture was more important and productive in the western Loess Plateau around 2000 cal bc.