Aim: The aim of this study was to investigate the effect of Bisphenoln A on osteogenic differentiation in bone marrow mesenchymal stem cells obtained from adult rat. Material and Methods: Rat bone marrow mesenchymal stem cells were extracted using the flashingout method. At the end of the third passage, cells were divided into groups of control and Bisphenol A treated with different doses of 1, 5, 10, 50, 100, 250, 500, 1000, 2000 and 4000 nM for period of 21 days in the osteogenic media containing 10% of fetal bovine serum. Then rate of Bone matrix mineralization, extracellular calcium deposition, expression of osteopontin and osteocalcin proteins was investigated during the procedure of osteogenesis. Data was analyzed using one-way ANOVA and the means difference was considered significant at p<0. 05. Results: A significant reduction in mean bone matrix mineralization, calcium deposition, expression and synthesis of osteopontin and osteocalcin was seen in the group of cells treated with Bisphenol A when compared to control group (p<0. 05) in a dose and time dependent manner. Conclusion: These results showed that Bisphenol A, as an environmental pollutant, cased a significant reduction in osteogenic differentiation in rat bone marrow mesenchymal stem cells; therefore, Bisphenol A can be considered as a reducing agent in cell differentiation.