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. 0mg / L Na2SeO3 respectively for 10 weeks, in order to observe the effects of different concentrations of selenite in drinking water on the urinary excretion of fluoride and renal damages induced by 150mg/ L NaF, and find out the optimal level of selenite in drinking water against fluoride toxicity. The results showed that fluoride could cause the significant elevation of fluoride ion levels in serum and urine of rats exposed to fluoride in drinking w ater and the obvious renal damages in pathology, enzyme histochemistry and ultrastructure. 2. 0mg / L Na2SeO3 in drinking water induced the most obvious acceleration of fluoride excretion in urine and possessed the most significant antagonistic effects on the renal impairments induced by 150mg / L NaF, those of 0. 5mg/ L Na2SeO3 were not evident, whereas 4.0 mg / L Na2SeO3 appeared to be toxic to kidney. Thus it is concluded that 2.0 mg/ L Na2SeO3 is the optimal concentration for the antagonistic effect on renal impairments induced by 150mg/ L NaF in drinking water .