The purpose of this study was to investigate the effect of a 12 week selective aerobic exercisetrial in water on bone density in obese postmenopausal women. Twenty obese post menopausalwomen as subject to participate in this study. Subjects randomly divided into a experimentaland control group.. Data analyzed with paired and independent samples T Test.The results of this study indicate that there was a significant increase in femoral bone density inexperimental group compared with control group in end of study period (P<0.05). Also; thelumbar spine bone density was increased moderately; but not significantly; in experimentalgroup.On the other hand;calcium and phosphorus levels were not different significantly betweenexperimental group and control group in end of study period (P<0.05).