OBJECTIVE: The purpose of this study was to evaluate the efficacy of alfacalcidol and calcium on the improvement of muscle strength in ambulatory elderly Thai women in age group of 65 or more who have hypovitaminosis D. MATERIAL AND METHOD: Seventy-two postmenopausal women age 65 years or more were enrolled to this study. Blood was collected from all participants for measured of 25(OH)D3, intact PTH and vitamin D receptor (VDR) genotypes. After blood collection, the quadriceps muscle strength was measured using the isokinetic dynamometer device. There were 42 subjects who satisfy the eligible criteria and agreed to participate in the experimental randomized controlled study. These subjects were randomized into two groups, one received calcium 1500 g/day combined with alfacalcidol 0.5 mg/day. Another group received calcium 1500 g/day with placebo. RESULTS: After 12 weeks of intervention, 40 subjects had the second muscle strength measurement (2 dropped out). By ANCOVA analysis, there were significant improvement of muscle strength in the group that received alfacalcidol compared to placebo in both 30 degrees/sec (20.28 vs.16.29, p = 0.025) and 60 degrees/sec (20.32 vs. 15.05, p = 0.002) angular velocities. CONCLUSION: Daily doses of 0.5 mg alfacalcidol with calcium effectively improved muscle strength in elderly Thai women who had low level of 25(OH)D3 compared to calcium alone.