Abstract: Objective To investigate anti-tumor activity of cerium nitrate in vivo and it's mechanism.Methods 60 Kunming(KM)mice were used in this experiment.To set up KM bearing H22 mice model by injecting tumor cells into left inguinal groove.Then the mice were treated with cerium nitrate(50,100,200 mg/kg)for two weeks.After that,inhibition ratio,thymus index,spleen index and stimulation index(SI)were calculated.The level of superoxide dismutase(SOD)and reduced glutathinoe(GSH)were detected with enzyme-chemical.Results The tumor weitht of three groups of cerium nitrate and C YT group were lower compared with negative control group(P<0101).The thymus indexes of cerium nitrate 50 mg/ kg and 100 mg/kg group were significantly higher than that of C YT group.The spleen index of cerium nitrate 100 mg/kg group was obviously higher than that of negative control group and C YT group(P<0105).Stimulation index of cerium nitrate 50 mg/kg group was obviously higher than that of negative control group(P<0101)and C YT group(P<0.05).The serum SOD level of cerium nitrate 50 mg/kg group was higher than that of negative control group(P<0.05)and C YT group(P<0.01).The GSH levels of cerium nitrate 200 mg/kg group notably higher than that of negative control gruop(P <0.05).Conclusion Cerium nitrate inhibits growth of tumor through activating immune functions of mice and promoting capabilities on anti-oxidation.