Abstract: In order to explore the effects of Dichlorfos on reproductive organ exponent and sex hormone levels in mature mice. 30 mature male mice were randomly divided into 5 groups. The 4 groups were experimental groups, treated with low (5.0 mg/kg), middle (10.0 mg/kg), high (20.0 mg/kg) and extremely high (40.0 mg/kg) doses of Dichlorfos for 16 consecutive days by gavage. The other was control group, treated with distilled water by gavage at the same volume. The testicle, epididymis and seminal vesicle indexes were weighted and the level of testosterone (T) was measured after 16 days. The results showed that, compared with control group, the epididymis and seminal vesicle indexes decreased significantly (P<0.05) in all experimental groups; the testicle index decreased significantly (P<0.05) in the middle, high and extremely high doses; T level of extremely high dose group was the lowest in the four experimental groups and decreased significantly (P<0.05). It was suggested that Dichlorfos could decrease mature male mice’s reproductive organ indexes and level of T, which consequently damage the mature male mice’s reproductive system.