AIM: To study the effect of fluoride on oxidative stress, DNA damage and apoptosis as well as cell cycle of rat oral mucosal cells and hepatocytes. METHODS: Ten male SD rats weighing 80-120 g were randomly divided into control group and fluoride group, 5 animals each group. The animals in fluoride group had free access to deionized water containing 150 mg/L sodium fluoride (NaF). The animals in control group were given distilled water. Four weeks later, the animals were killed. Reactive oxygen species (ROS) in oral mucosa and liver were measured by Fenton reaction, lipid peroxidation product, malondialdehyde (MDA), was detected by thiobarbituric acid (TBA) reaction, reduced glutathione (GSH) was assayed by dithionitrobenzoic acid (DTNB) reaction. DNA damage in oral mucosal cells and hepatocytes was determined by single cell gel (SCG) electrophoresis or comet assay. Apoptosis and cell cycle in oral mucosal cells and hepatocytes were detected by flow cytometry. RESULTS: The contents of ROS and MDA in oral mucosa and liver tissue of fluoride group were significantly higher than those of control group (P < 0.01), but the level of GSH was markedly decreased (P < 0.01). The contents of ROS, MDA and GSH were (134.73 +/- 12.63) U/mg protein, (1.48 +/- 0.13) mmol/mg protein and (76.38 +/- 6.71) mmol/mg protein in oral mucosa respectively, and (143.45 +/- 11.76) U/mg protein, (1.44 +/- 0.12) mmol/mg protein and (78.83 +/- 7.72) mmol/mg protein in liver tissue respectively. The DNA damage rate in fluoride group was 50.20% in oral mucosal cells and 44.80% in hepatocytes, higher than those in the control group (P < 0.01). The apoptosis rate in oral mucosal cells was (13.63 +/- 1.81) % in fluoride group, and (12.76 +/- 1.67)% in hepatocytes, higher than those in control group. Excess fluoride could differently lower the number of oral mucosal cells and hepatocytes at G0/G1 and S G2/M phases (P < 0.05). CONCLUSION: Excess fluoride can induce oxidative stress and DNA damage and lead to apoptosis and cell cycle change in rat oral mucosal cells and hepatocytes.