Abstract: Objective To study the effects of fluoride on expression of calmodulin(CaM)in rat osteoblasts cultured in vitro in different doses and at different time.Methods Osteoblasts were isolated from the calvariae of new-born Wistar rats by means of bone tissue block,and cultured with DMEM.Different concentrations of fluoride were added to rat osteoblasts and incubated for differenthours(24 hours,36 hours and 48 hours).The expression of CaM was analyzed with immunohisto-chemical stain.Results At 24 hours,0.5 mg/L fluoride significantly increased the expression of CaM in rat osteoblasts,but 2 mg/L fluoride decreased it.At 36 hours,the expression of CaM was higher in 2 mg/L fluoride group and lower in 8 mg/L fluoride group than that in control group(P<0.05).At 48 hours,the expression of CaM in all fluoride groups were significanthigher than that in control group(P<0.05).Conclusion The fluoride effect on the expression activity of CaM in osteoblasts is dose-and time-dependent and the effect of inhibiting is ahead of the effect of stimulating.