Fluoride is one of the most potent stimulators of bone formation in vivo. But its direct effects on osteoblast is not yet clear. This study was to investigate the effects of Sodium fluoride on alkaline phosphatase(ALP) activity, cAMP formation responsive to parathormone(PTH) and type I α 2 collagen ribonucleic acid (mRNA) level in Murin osteoblast-like (MC3T3-E1) cells. The cells were cultured in α-Minimal essential medium (α-MEM) supplement with 10% fetal bovine serum (FBS) and then changed to 0.1% FBS with various concentration of Sodium fluoride. The ALP activity was assayed by the method of Lowry with disodium phenyl phosphated as substrate. cAMP formation was measured by Radioimmuno Assay(RlA). Type I α 2 collagen ribonucleic acid(mRNA) expression was studied by Nothern blot analysis. The results were as follows : 1. cAMP level was increased by PTH in MC3T3-E1 cells. 2. Sodium fluoride showed the tendency of inhibitory effects on cAMP responsiveness to PTH in MC3T3-E1 cells. 3. Sodium fluoride increased ALP activity at cocentration of 2µM, 4µM, and 10µM significantly different from control at the 0.001 level. ALP activity revealed maximum value at 10µM in this study. 4. Nothern blot analysis of Sodium fluoride treated cells, using Type I α 2 collagen prove, revealed significant increase at 10µM in MC3T3-E1 cells.