This study investigates the Mid-Pleistocene paleoenvironment and dietary behaviour of ancient herbivores in the South African central interior, today part of the semi-arid Kalahari savanna. Analyses were undertaken of carbon (delta C-13) and oxygen (delta O-18) stable isotopes in tooth enamel carbonate of twelve fossil herbivore species from Layers 4b and 4a, associated with Earlier Stone Age (ESA) and transitional ESA-Middle Stone Age (Fauresmith) industries respectively, at the archaeological site of Kathu Pan 1. The data are compared with other Eearly to Mid-Pleistocene herbivore assemblages located in the central interior, namely Cornelia-Uitzoek, Wonderwerk Cave and the Florisbad Spring. Results indicate that the median delta C-13 values for all ungulate taxa at Kathu were >-4 parts per thousand, indicating predominantly C-4 based diets, although in certain taxa, some individuals included a significant C-3 component in their diet. The delta O-1(8) values of most species at Kathu were relatively low, suggesting a cooler and/or wetter climate. Carbon isotope evidence for C-4 dominated habitats at Kathu, but with a larger C-3 component amongst grazers than today, resembles the other Early to -Mid-Pleistocene assemblages in the region. Similarly, delta O-18 values for Kathu supplement existing evidence that the region was substantially wetter than in modern times.