Abstract: Objective To observe the influence of coal-burning fluorosis on activity of nitric oxide synthase (NOS) and content of nitric oxide (NO) in rat brain tissue.Methods Twenty-four Sprague-Dawley (SD) rats were randomly divided into a control group and low- and high-fluoride exposure groups.The rats in low- and high-fluoride exposure groups were fed for 6 months continuously with the corn polluted during drying process due to the burning of high fluoride coal from endemic fluorosis areas to establish an animal fluorosis model.By the end of the treatment,fluoride contents in urine and brain tissue of the rats were detected with fluorine ion selective electrode;NOS activities were determined with photometric method and NO contents were measured with nitrate reductase method.Results Compared with the control rats,the rats exposed to low- and high-fluoride exhibited significantly higher fluoride content in urine (2.87±0.12 and 5.27±0.15 vs.1.68±0.02 mg/L) and brain tissues (1.14±0.04 and 1.79±0.04 vs.0.52±0.05 mg/kg) and significantly higher NO content in brain tissues (3.13±03 and 4.25±0.66 vs.2.29±0.46 μmol/L) (P<0.05 for all).The activity of inducible NOS (iNOS) in brain tissues of the rats with low-fluoride exposure was significantly higher than that of the control rats (8.04±3.90 vs.4.02±0.20 kU/g) (P<0.05).Conclusion Chronic fluorosis could be induced in rats fed with the corn polluted during drying process by burning of high fluoride coal from endemic fluorosis areas and iNOS activity and NO content in brain tissues could increase in the rats with coal-burning fluorosis.