To investigate the effects and possible mechanisms of the action of fluoride on testis cell cycle and cell apoptosis in male mice, sexually mature male Kunming mice were exposed to 50, 100, 200, and 300 mg NaF/L in their drinking water for 8 weeks. At the end of the exposure peri ods, sperm quality, the percentage of G1/ G0 (Gap 1/Gap 0), S (synthesis), G2/M (G ap2/M, minosis), and apoptosis rate in testicle cells were measured using flow cytometry. Serum and testicular testosterone levels were determined with a radio immunoassay (RIA) kit. Effects on sperm quality and oxidative stress were also observed. Different dosages of NaF also altered the changes in the testicular cell cycle. Compared to the control, the testicular cell cycle of mice drinking 50 or 100 mg NaF/L was not significantly affected (P>0.05). However, with the higher NaF concentrations of 200 and 300 mg/L, the percentage of cells in G1/G0 phase increased significantly (P <0.01), whereas those in S phase decreased significantly (P<0.01). On the other hand, the percentage of cells in G2/M phase was similar to that of the control. In the two higher NaF concentration groups, distinct cell apoptosis of testis was observed. Likewise, sperm quality and antioxidant defenses were significantly reduced and oxidative stress occurred, whereas these effects were only slight at the lower NaF concentrations. Serum and testicular testosterone levels were also significantly lower at 100, 200, and 300 mg NaF/L (P<0.01), compared with the control group.