The spatiotemporal pattern of the late Cenozoic spread of C-4 vegetation is an important indicator of environmental change that is intertwined with the uplift of the Himalaya and Tibetan Plateau, and the development of the East Asian monsoons. To explore the spread of C-4 vegetation in China and shed new light on regional climatic evolution, we measured delta C-13 values of more than 200 small mammal teeth (primarily rodents and lagomorphs) using a laser ablation isotope ratio mass spectrometry approach. Small mammals are highly sensitive indicators of their environment because they have limited spatial ranges and because they have minimal time-averaging of carbon isotope signatures of dietary components. The specimens originate from four classic Late Miocene fossil localities, Lufeng, Yuanmou, Lingtai, and Ertemte, along a southwest-northeast transect from Yunnan Province to Inner Mongolia. In Yunnan (Lufeng, Yuanmou) and on the Loess Plateau (Lingtai), the small mammal delta C-13 values record nearly pure C-3 ecosystems, and mixed but C-3-based ecosystems, respectively, in agreement with previous studies based on carbon isotopes of large herbivores and soil carbonates. In Inner Mongolia, the micromammalian tooth enamel delta C-13 record picks up the presence of C-4 vegetation where large mammal samples do not, indicating a mixed yet C-3-dominated ecosystem at similar to 6 Ma. As a whole, the results support a scenario of northward increasing C-4 grass abundance in a pattern that mirrors northward decreasing precipitation of the summer monsoon system. The results highlight differences between large and small mammals as indicators of C-4 vegetation in ancient ecosystems, particularly the ability of small mammal delta C-13 values to detect the presence of minor components of the vegetation structure. (C) 2015 Elsevier B.V. All rights reserved.