OBJECTIVES: The purpose of this study was to evaluate the effects of oral 25(OH)D on vitamin D related bone metabolic factors and adverse events in Korean postmenopausal women with osteopenia and osteoporosis. METHODS: A total 60 women from outpatient Department of Endocrinology and Metabolism were enrolled in this study. A phase IV clinical trial was conducted in which a randomized double-blind, placebo-controlled study with calcifediol (Caldiol(R), 20microg daily; Medica Korea Co., Ltd., South Korea) or placebo for 8 weeks. Serum 25-hydroxyvitamin D and parathyroid hormone levels were measured at 0, 4, and 8 weeks and adverse events were monitored. RESULTS: In the calcifediol group, the serum 25-hydroxyvitamin D levels were>75 nmol/L in 90.3% of the subjects at 8 weeks, and significantly higher compared with the placebo group (102.1+/-32.0 vs. 31.5+/-12.0 nmol/L; P<0.0001). Although the serum PTH level was significantly decreased after 8 weeks in the calcifediol group (P<0.01), there was no significance when compared with the placebo group (21.1+/-7.7 vs. 25.6+/-12.7 pg/mL; P=0.234). There was no drug-related adverse event. CONCLUSION: Oral calcifediol improved serum 25-hydroxyvitamin D status without drug-related adverse events in Korean postmenopausal women with osteopenia and osteoporosis.