Objective: This study was designed for determination of the additional effect of alendronate to ongoing hormone replacement therapy in postmenopausal women. Methods: Alendronate (10mg/day, orally) was added in 66 postmenopausal women with estrogen replacement therapy who were taken HRT more than 2 years previously. The patients were followed up for 1 year thereafter. We measured bone mineral density and bone turnover markers (osteocalcin, ALP, D-Pyridinoline/Cr) at that time prior to HRT, 1 year, 2 year after HRT and 1 year after combination of alendronate therapy. Results : The BMD(g/㎠) of L2-4 were 1.09±2.44(T-score -2.86±0.69) prior to HRT, 0.82±0.07(T-score -2.53±0.49) 1yr after HRT, 0.80±0.11(T-score -2.61±0.92) 2yr after HRT, and 0.88±0.08(T-score -2.05±0.70) after combination therapy. Serum osteocalcin(ng/ml) level were 30.3±14.8, 21.09±14.09, 17.31±8.46, and 10.85±9.09 respectively. Dpd/Cr(nmole/mmole) were 7.0±4.5, 5.82±0.91, 5.29±2.15, and 4.22±0.61. From these results, we can observe more significant increase of BMD and decrease of bone turnover rate following combined therapy rather than HRT only. Conclusion: This study shows that the addition of alendronate is beneficial in postmenopausal women with ongoing estrogen replacement therapy by preventing or treatment of osteoporosis.