The genetic toxicity of tetrandrine on mice was studied by sperm deformity test,marrow micronucleus test and sister chromatid exchange. The results showed that the rate of spermatic deformity and marrow cells micronucleus in mouse was increased significantly in growps treated with tetrandrine, and there was dose response relationship, but the change of the frequencies of sister chromatid exchanges was not obvious. It is concluded that tetrandrine has genetic toxicity to experimental animal.