Abstract: Objective To study the role of nuclear factor of activated T cell 1(NFATc1) in the osteoclasts of rats with skeletal fluorosis caused by chronic fluorosis.Methods Thirty-six Sprague-Dawley rats were randomly divided into three groups according to their body weight(12 in each group,half male and half female):control group(sodium fluorideNaF<0.5 mg/L),low-dose fluoride group(5.0 mg/L NaF),high-dose fluorosis group(50.0 mg/L NaF).The rats were sacrificed after 8 months of fluoride treatment.The number of osteoclast inside the distal femur of the rats was counted by tartrate-resistant acid phosphatase staining(TRAP),and the protein and mRNA levels of NFATc1 inside the distal femur of the rats were detected by immunohistochemistry and in-situ hybridization.Results NFATc1 positive osteoclasts were observed.Compared to the control group(135.90?1.03,110.45?1.55),the protein and mRNA expressions of NFATc1 were higher(156.81?1.26,132.50?1.58)in the low-dose fluoride group(135.46?1.19,110.26?1.37)(P<0.05),but decresed in the high-dose fluoride groups(P>0.05).Conclusion NFATc1 may play an important role in osteoclasts differentiation and regulation in the skeletal fluorosis caused by chronic fluorosis.