Objective: To investigate the hepatoprotective effect and its circadian variations of Xiaoyao Powder and the possible mechanisms for protection on liver injury in rats. Method: The rat model of liver injury was induced by subcutaneous injection of 40% CCl4 .The rats were given Xiaoyao Powder by gavage in the morning or evening for 12 days. General behavior state

body weight change

the levels of ALT

AST in serum and SOD and MDA activites in liver homogenate were detected.The pathology of liver was observed. Result: Compared with the model group

the Xiaoyao Powder was found to significantly improve the body weight and general behavior state

reduce the serum levels of ALT

AST and MDA

increase the activity of SOD

improve the pathological changes of liver tissue.Meanwhile

evening administration and the low dose was displayed a very good effect in most of the indexes. Conclusions: Xiaoyao Powder shows significant protective action on liver injury in rats.The effect of Xiaoyao Powder may be closely related to administration time.