Abstract: Objective To study the mechanisms of the antagonistic action of selenite on flouride-induced male reproductive damages,and find out the optimal level of selenite in drinking water against fluoride toxicity.Methods Five groups of SD male rats were provided with deionized drinking water containing 0 and 150mg/L NaF,and containing both 150mg/L NaF and 0.5,2.0 or 4.0 mg/L Na₂SeO₃ respectively for 8 weeks,observing the levels of fluoride in blood and urine as well as the impairments of testis and epididymis of rats induced by 150mg/L NaF.Results Flouride could cause the elevation of flourine concentrations in blood and urine,the abnormalities of trace elements in serum and testis,as well as the significant increase of lipid peroxide(LPO) levels,and the obvious decreases of activities of glutathione peroxidase(GSH-Px)and ATPase in testis and epididymis of rats exposed to fluoride in drinking water.2.0mg/L Na₂SeO₃ in drinking water induced acceleration of fluoride excretion obviously in urine and possessed the certain adjustment of changes of trace elements in serum and testis,the most significant antagonistic effects of increases of LPO levels and decreases of GSH-Px and ATPase activities in testis and epididymis of rats exposed to fluoride,those of 0.5 and 4.0 mg/L Na₂SeO₃ were not powerful.Conclusion Na₂SeO₃ of 2.0mg/L is the optimal level for the antagonistic effect on testis and epididymis impairments.