Temperature is the single most important environmental factor affecting many biological processes in organisms. Ectotherms are viable under a wide range of body temperatures, but their physiological processes and behavioral performances are usually maximized at moderate to relatively high body temperatures. We collected Qinghai toad\|headed lizards (Phrynocephalus vlangalii; Agamidae) in August 2005 from a population in Qinghai (northwestern China) and used adults to study selected body temperature (Tsel), thermal tolerance \[critical thermal minimum (CTmin) and critical thermal maximum (CTmax)\] and the thermal dependence of food assimilation and locomotor performance. Tsel was measured on a laboratory thermal gradient ranging from 18 ℃ to 60 ℃ (20 mm above the terrarium floor); CTmin and CTmax were determined in an incubator, with lizards being cooled or heated from 28 ℃ at the rate of 0.25 ℃ per minute and more slowly when temperatures inside the incubator were lower than 5 ℃ or higher than 40 ℃. We did not find between\|sex differences in Tsel, CTmin and CTmax, and thus pooled data for both sexes. The mean values for Tsel, CTmin and CTmax were 33.3 ℃, 0.9 ℃ and 46.9 ℃, respectively. Within the range from 27 ℃ to 35℃, body temperature affected daily food intake but had no important role in influencing apparent digestive coefficient and assimilation efficiency. Thus, consistent with the results reported for a wide range of lizard taxa, our data show that digestive performance is less sensitive to variation in body temperature in P. vlangalii. The number of stops in the racetrack decreased with increase in body temperature within the range from 17 ℃ to 39 ℃, and then increased at 41 ℃. Sprint speed increased with increase in body temperature within the range from 17 ℃ to 39 ℃, and then decreased at 41 ℃. The mean values for the length of continuous locomotion were overall greater at higher body temperatures (29-41℃) than at lower temperatures (17-27 ℃). Overall, body temperatures within the range of 33-41 ℃ were optimal for locomotion. When comparing our data with those reported for temperate and warm\|climate lizards, we found that body temperatures maximizing locomotor performance are relatively high in P. vlangalii. Our data support the idea that Tsel represents the body temperature at which numerous processes function at a relatively high level, as revealed by the fact that Tsel fell within the range of temperatures optimal for locomotor performance in P. vlangalii. Inter\|specific comparisons reveal that lizards using different habitats and occupying different geographic (climatic) regions differ in both CTmin and CTmax. Overall, CTmin is greater in lizards using warmer habitats or living in warmer localities, and CTmax is greater in lizards using opened habitats. Qinghai toad\|headed lizards are typically found in open spaces in arid or semi\|arid regions covered sparse vegetation. The region occupied by P. vlangalii is climatically severe, where daily and seasonal fluctuations in ambient temperature are very pronounced. Thus, the enhanced ability to tolerate temperature extremes seen in P. vlangalii is likely determined evolutionarily as a consequence of adaptation to local thermal conditions.