In order to explore effects of senium on metabolism of active oxygen radicals in liver and kidney of rats with fluorosis,2 groups of Wistar rats were fed with normal fodder and high concentration of NaF water (1.58, 2.63 mmol/L fluorine,F).2 groups were fed with selenite fodder (2.0 mg/kg selenium,Se) and high F. At the same time,2 groups were fed with normal fodder and high F for 7 months,then 2.0 mg/kg Se were supplemented in fodder.The contents of free radicals (FR) in liver and kidney were demonstrated by means of the technique of electronic spin resonance (ESR),the contents of Se and F,the activities of glutathion peroxidase (GSH-Px), superoxide dismutase (SOD) and the contents of lipid peroxidase (LPO)in liver and kidney were tested in 14 months.The results showed that there was an increase of F,FR and LPO and a decrease of GSH-Px and SOD in rats with fluorosis. When Se was given in the different time of fluorosis, F lowered, the signal of FR weekened,LPO lessened,GSH-Px and SOD recovered.It indicated that Se not noly could antagonize high F but could rectify metabolic disorders of FR in rats with fluorosis.