Objectives: Vitamin D inadequacy was defined previously by the occurrence of osteomalacia and rickets. However, at present, the risk of secondary hyperparathyroidism creates the basis for the term vitamin D inadequacy, as this mainly asymptomatic condition enhances the risk of osteoporosis and skeletal fractures. The aim of the present study was to examine the effect of oral vitamin D supplement in Vitamin D inadequacy.Methods: Vitamin D inadequacy were treated with calcium 600mg and cholecalciferol 400IU(Cal-D-Vita) for 3, 6, 12months. Serum 25(OH)D3 and PTH were checked at 3, 6, 12months. Results: Vitamin D therapy significantly increased serum 25(OH)D3 at 3 month and had tendency to increase at 6 and 12 months. Vitamin D therapy significantly decreased serum PTH at 3 month and had tendency to decrease at 6 and 12 months. Conclusion: Supplementation of Vitamin D increased serum 25(OH)D3 and decreased serum PTH in vitamin D inadequate patients.