Abstract: AIM: To study the effects of estrogen on stimulating bone formation in osteoblast-like cell line TE85. METHODS: Utilizing methods of ³H-thymidine incorporation for cell proliferation, ³H-proline incorporation for collagen synthesis, ultraviolet spectrophotometry for measurement of alkaline phosphatase (ALP) activity, radioimmunoassay for bone gla-protein (BGP) content assay, and radio-ligand binding for estrogen receptor assay. RESULTS: Cells were incubated with various concentrations (from 0.01 to 10 nmol.L^-1) of 17β-estradiol (E₂) for 48 h and 72 h, ³H-thymidine incorporation into DNA was increased gradually while ³H-proline incorporation was enhanced in the same fashion. E₂ at the same dose increased the intracellular ALP activity and BGP content at the same time. In ligand-receptor binding experiment, the KD of ³H-E₂ saturation test was 2.59×10^-10 mol.L^-1 in TE85 cells and the receptor number was found to be 262.7±64.6 site per cell. The IC₅₀ of 4-OH-tamoxifen and ICI 182,780 were 0.99×10-8 mol.L^-1 and 8×10-10 mol.L^-1, respectively. CONCLUSION: E₂ improved bone formation by ways of stimulating cell proliferation, enhancing collagen synthesis, ALP activity, and BGP content. The effects of E₂ were performed by the mediation of estrogen receptor.