Objective: To study the mechanisms of the antagonistic action of selenite on fluoride-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 150 mg/L NaF, and containing both 150 mg/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 150 mg/L NaF. Results: Fluoride could cause the elevation of fluorine 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. 2.0 mg/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 2.0 mg/L is the optimal level for the antagonistic effect on testis and epididymis impairments.