We collected adult Eremias argus (Lacertidae) from a population in Yangquan (Shanxi, northern China) to study thermal dependence of food assimilation and sprint speed. Selected body temperature (Tsel) measured on a laboratory thermal gradient was 36. 0℃; critical thermal minimum (CTMin) and critical thermal maximum (CTMax) averaged 1. 0℃ and 44.9℃ , respectively. Differences in Tsel, CTMin and CTMax were not found between-sex. Within the range of body temperatures considered, food passage time, daily food intake, daily production of feces and urates, apparent digestive coefficient (ADC) and assimilation efficiency (AE) were all affected by body temperature. Food passage time decreased with increase in body temperature within the range from 26℃ to 34℃ , and then increased at higher body temperatures. Lizards at 30, 32, 34 and 36℃ ate more food and produced more feces and urates than did those at 28℃ and 38℃ . Although ADC and AE were both higher at 34℃ and 36℃ than at other lower or higher temperatures, no clear patterns associated with temperature could be discerned for these two variables. Sprint speed increased with increase in body temperature within the range from 18℃ to 36℃ , and then decreased at 38℃. The body temperatures maximizing sprint speed was around 36℃, which was much close to the mean value of body temperatures selected by lizards on the thermal gradient. This result adds evidence that the range of optimal body temperatures for sprint speed is tightly coupled with Tsel in lizards [Acta Zoologica Sinica 52 (2): 256 - 262, 2006].