Objective：To observe the anti-tumor activity of oxymatrine alone or in combination with cyclophosphamide against Lewis lung carcinoma in mice and to discuss the related mechanisms. Methods: Lewis lung carcinoma cells were transplanted subcutaneously to establish cancer transplantation model in mice. Animals were orally given oxymatrine(80, 40 and 20 mg/kg) alone or in combination with cyclophosphamide(30 mg/kg, gastric lavage). The mean tumor inhibitory rate was calculated and the growth curve of tumors was plotted. Radio immunoassay(RIA) was used to determine the serum concentration of epidermal growth factor (EGF). Comparison was made between the treatment groups and the control group. Results: The inhibitory rates were not significantly different between the control group and the pure oxymatrine treatment group. When combined with cyclophosphamide, the inhibitory rates of oxymatrine were significantly increased (P＜0.01). When at 80, 40 and 20 mg/kg, oxymatrine inhibited tumor growth by 66.62%, 61.70% and 59.04%, respectively. Also, when combined with cyclophosphamide, oxymatrine at 40 and 80 mg/kg significantly decreased EGF levels compared with those of model group and pure oxymatrine groups (P＜0.01). Conclusion: Oxymatrine can enhance the inhibitory effect of cyclophosphamide against Lewis lung carcinoma, and the mechanism may be related to the decrease of serum EGF level.