To observe the anti-tumor effect of the water extracts from Manchurian walnut.Methods:To study the effect of the water extracts on S180, H22, LWS modeled mice, on weight maintaining of body, thymus, and spleen so as to explore the anti-tumor mechanism.Results:Water extracts of Manchurian walnut has potent tumor inhibiting action, and significant protection on weight of body, thymus, and spleen.Conclusion:Water extracts of Manchurian walnut may combat tumor by improving body's disease resistance and immune system.