A population of Lacerta agilis was collected in May 2013 in Xinjiang, China for the study. These adult lizards were fed and bred in the laboratory and the diurnal change of their body temperature was examined during November to December, 2013. The correlation of body temperature using the direct measurement of cloaca temperature and morphological characteristics such as snoutvent length (SVL) and weight was analyzed, and the effects of ambient temperature on the physiological thermoregulation ability of lizards with different ages and sexes were discussed. The results showed that body temperature had a significant diurnal rhythm and was (0.89±0.16) SymbolpB@C higher than environment temperature under room temperature condition (18-22) ℃. Body temperature had no significant differences between the sexes and showed no significant correlation with SVL and weight of the lizard. However, body temperature and ambient temperature had a positive, linear correlation. The isothermal point of y=kx+b and y=x was very important to the regulation of body temperature. Body temperature of the lizard was lower than ambient temperature when ambient temperature was higher than the isothermal point. On the contrary, it was higher when ambient temperature was lower than the isothermal point. Physiological thermoregulation ability of the larval lizard was stronger, while that of the female was weaker. The relationship of diurnal regulation of body temperature with ambient temperature was found in the study, however, the relationship between physiological and behavioral adjustment of lizard body temperature needs further research.