Abstract: The aim of this research was to investigate the preventive role of light activity and to determine effectiveness of weight-bearing activity or specific strengthening exercise on bone mass in postmenopausal women. Twenty-five postmenopausal women participated in this study. They had been diagnosed clinically and also their lumbar spine bone density was measured by Dual Energy X-ray Absorbtiometry (DEXA) as normal, osteopenic or osteoporotic. Twelve women received 30 min walking as a weight-bearing activity and 13 women performed specific strengthening exercise for back extensors and postural exercise twice a day for 6 months. Bone density of both groups were measured before and after the treatment. Considering the post-treatment T values, it was found that Bone Mineral Density (BMD) was increased in 50% of women from the walking group and 53.8% of women from the exercise group; nevertheless this was not statistically significant. Although BMD values showed similar changes in both groups, they were significantly decreased in the exercise group (p<0.05). This study reveals that walking and specific strengthening exercise have no effect in the prevention of bone mass in postmenopausal women if they are applied as light activities (1-3 MET). Although there is similar decrease in both walking and specific strengthening exercise groups after treatment, the decrease in exercise group was found significant.