Abstract: The aim of this study was to investigate the protective effect of instant powder of Cordyceps militaris on liver injury induced by cyclophosphamide in mice. Kunming mice were randomly divided into normal group, model group, positive control group, high dose group (80 mg/kg), middle dose group (40 mg/kg)and low dose group (20 mg/kg). The hepatic injury model of mice was established by intraperitoneal injection of cyclophosphamide (80 mg/kg), then the mice of normal and model group were fed with normal saline, mice of positive control group were fed with silybin and the mice of dosage groups were fed with different dosage of instant powder of Cordyceps militaris. Alanine aminotransferase (ALT), aspartate aminotransferase (AST), interleukin-2 (IL-2), tumor necrosis factor alpha (TNF-α)of serum in mice and superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GSH-Px)and malondialdehyde (MDA)level of liver tissue in each group mice were determined by reagent kit method. Experimental results showed that ALT and AST activity of serum in mice of every dosage group significantly decreased (p<0.01)comparing with the model group. For male mice, the activities of SOD and GSH-Px of liver tissue in mice of every dose group were significantly increased (p<0.01), and the content of MDA was decreased significantly (p<0.01), but only the CAT activity in mice of middle and high dose groups was higher than the model group (p<0.01). For female mice, the activity of SOD and GSH-Px in mice of middleand high dosage group was higher than model group dramatically (p<0.01), the dramatic differences in activity of CAT and the content of MDA existed between the dosage groups and the model group (p<0.01). In addition, the instant powder of Cordyceps militaris could significantly increase the content of interleukin-2 (IL-2)in every group and could increase the content of TNF-α in middle and high dosage group compared with the model group (p<0.01). So the instant powder of Cordyceps militaris has protective effect on cyclophosphamide-induced hepatic injury in mice.