Background: Patients who have been submitted to bariatric surgery are prone to bone mass abnormalities caused by restriction of calcium intake associated with malabsorption of both calcium and vitamin D. Reduced calcium absorption is secondary to the exclusion of duodenum and proximal jejunum where calcium is maximally absorbed. Aerobic weight bearing exercise is more adapted to improve bone mass over whatever viable physical activity, they assume a double part over stressing the bones as they set both gravitational and muscular stress on bones. Objective: To determine the effect of aerobic exercises in prevention of bone mass loss post bariatric surgeries. Patients and Methods: Thirty female patients with post bariatric surgeries participated in this, their ages were between 25 to 45 years selected from Shebin El-Kom Hospital, Menoufia and randomly distributed into two equal groups: Group A (Study group): included 15 patients who received 30 minutes of aerobic exercise through walking on treadmill, in addition to conventional medical care 3 days per week and group B (Control group): included 15 patients who were on their conventional medical care. Results: There was no significant difference in T score of spine (L2-L4), femoral neck and total femur between both groups pre-treatment (p > 0.05). Comparison between both groups post treatment revealed a significant increase in T score of spine (L2-L4), femoral neck and total femur of the study group compared with that of the control group (p > 0.001). Conclusion: It can be concluded that aerobic exercises had fruitful effects in cases of osteoporosis patients after bariatric surgery as evidenced by the significant increase in BMD and T-score mean, so decrease risk of fractures and enhance physical performance.