Objective To explore the role of apoptosis-inducing factors (AIF) mediated non-apoptosis classic pathway involved in neuron apoptosis of rats with chronic fluorosis.Methods Sixty Sprague Dawley (SD) rats (body weight 100-120 g) were divided into two groups (30 rats in each group,half male and half female) by random number table according to body weight.Control group was fed with tap water with fluoride content ＜ 0.5 mg/L and fluorine group was fed with water with fluoride content of 50.0 mg/L.Both groups were fed with standard food with fluorine content ＜ 0.5 mg/kg.After 10 months,all the animals were sacrificed though heart perfusion using phosphate buffer,and brain tissue was taken.Immunohistochemical method was employed to detect the distribution of AIF in brain tissue.Western blotting was used to test the protein expression of AIF,cl-caspase-3 and cl-caspase-9.Flow cytometry was used to examine apoptosis rate.Results The AIF positive distribution and degree of staining in the neurons of hippocampal CA1,CA2 and CA3,as well as the parietal cortex (7.50 ± 2.17,9.00 ± 1.63,8.00 ±0.82,10.24 ± 1.80) in rats with chronic fluorosis were significantly higher than those of the control group (5.18 ±1.66,6.27 ± 1.42,6.36 ± 1.96,6.96 ± 2.62,t =2.76,4.09,2.45,5.77,all P ＜ 0.05).The AIF protein expression of neuronal mitochondria in the cerebral tissue of rats with chronic fluorosis [(89.46 ± 8.47)％] was significantly lower than that of the control group [(100.00 ± 7.12)％,t =3.16,P ＜ 0.01],while the AIF protein expression of the neuronal nucleus [(112.80 ± 7.10)％] was significantly higher than that of the control group [(100.00 ± 8.20)％,t =3.75,P ＜ 0.01];cl-caspase-3 and cl-caspase-9 protein expression in the neurons of hippocampus and cortex from the rats with chronic fluorosis [(132.14 ± 18.66)％,(107.31 ± 2.58)％,(121.33 ± 14.86)％,(112.97 ± 7.97)％]were significantly higher than those of the control group [(100.00 ± 11.99)％,(100.00 ± 3.74)％,(100.00 ± 16.87)％,(100.00 ± 8.04)％,t =3.55,3.94,2.32,2.81,P ＜ 0.01 or ＜ 0.05].As compared with those of the control group [(1.28 ± 0.59)％,(1.88 ± 0.25)％],the apoptosis rates in hippocampus and cortex of the rats with chronic fluorosis [(2.55 ± 0.58)％,(3.05 ± 0.65)％] were significantly increased (t =3.08,3.40,all P ＜ 0.05).Conclusion Both of AIF-mediated caspase-independent apoptosis and the classic caspase-dependent apoptosis pathways have participated in neuron apoptosis in rat induced by chronic fluorosis,which may be one of the mechanisms of brain damage of the disease.