Abstract: Objective To explore morphological changes of bone in the progress of coal-burning fluorosis in rats.Methods Rat coal burning fluorosis model was established under low-protein and low calcium;the contents of 24-hour urinary fluoride,bone fluoride,dental fluorosis were determined to judge the degree of the injury;bone mineral density of femur and tibia was determined using X-ray absorptiometry;morphological changes of femur cancellous bone ultrastructure was observed with scanning electron microscope and morphogenetic changes of the tibia bone were detected with static measurement parameters.Results All rats in fluoride groups had dental fluorosis.Bone fluoride content(199.90±106.84 mg/kg) and bone mineral density(0.205 3 g/cm²) of fluoride groups were significantly higher than those of control group(30.06±6.11 mg/kg and 0.185 4 g/cm²),with statistically significant differences(P<0.05 for all).Morphometry showed that trabecular area of upper tibia of the rats in fluoride groups(67 612.02±1 662.23 mm²),trabecular bone perimeter(7 655.44±918.05 mm),and the number of trabecular bone(38.25±4.99/mm) were significantly higher than those of the rats in control group(50 951.43±9 046.88 mm²,5 172.42±789.70 mm,and 27.75±4.19/mm;P<0.05 for all).Conclusion Under low-protein and low calcium condition,excessive fluoride exposure can lead to pathological changes of bone,especially the changes of osteomalacia in rats based on histomorphometric study.