Objective: The purpose of this prospective study is to investigate the impact of adding active vitamin D metabolite to hormone replacement therapy (HRT) in the treatment of osteoporosis in early postmenopausal women. Methods: Fifty-two naturally postmenopausal women receiving either 0.625 mg conjugated estrogen with 2.5 mg medroxyprogesterone acetate daily for 12 months or 0.50 µgr one alpha cholecalciferol in addition to 0.625 mg conjugated estrogen with 2.5 mg medroxyprogesterone acetate daily for 12 months. Results: Bone mass density (BMD) increases significantly in both treatment groups at 12 months not only in proximal femur but in the lumbar spine as well. In the HRT + alpha calcidiol group, the percentage of change in BMD for the proximal femur was 17.32±22.41 and 15.02±10.05 for the lumbar spine. In the HRT alone treatment group the percentage of change in BMD was 12.21±12.81 and 9.44±8.01 for the proximal femur and the lumbar spine respectively. Conclusion: Addition of vitamin D metabolite seemed to potentiate the BMD elevating effect of HRT even though the positive trend in the BMD change was not statistically significant in one year.