OBJECTIVE: To study the damages of fluoride on the male reproductive system in rat testes. METHODS: A total of 30 male SD rats were randomly divided into control group, high, low dose fluorine treated groups, which were given normal saline ,20 mg/kg sodium fluoride, and 10mg/kg sodium fluoride respectively. After 39 days the change of the weight of rats and the number of sperms were observed. The change of telomerase reverse transcriptase(TERT) and proliferating cell nuclear antigen (PCNA) were observed by using in situ hybridization and radioimmunoassay respectively. RESULTS: The weight was (273.39 +/- 20.68), (240.00 +/- 21.39) g in NaF treated groups, which was lower than that in control group(P < 0.05); The rate of TERT expression in germ cells of testes in NaF treated groups was (13.89 +/- 4.86)% and (6.33 +/- 4.42)% respectively, which was significantly lower than that in control group (P < 0.05). The rate of PCNA expression in germ cells of tests in NaF treated groups was (0.71 +/- 0.05)%, (0.60 +/- 0.08)% respectively, which also was significant lower than that in control group(P < 0.05). The number of sperms was (18.31 +/- 1.20)10(10)/L, (9.17 +/- 1.38)10(10)/L, which was lower than that in control group (P < 0.05). CONCLUSION: Fluorine possibly damages the male reproductive system by reducing the expression of TERT and PCNA.