The aim of this single-center, open-label, non-controlled randomized study was to evaluate which formulation of vitamin D between cholecalciferol and calcifediol is most effective in the treatment of hypovitaminosis D in older adults. Demographic characteristics, clinical history and comprehensive geriatric assessment were recorded at admission. Eligible patients randomly received an equivalent vitamin D supplement either with cholecalciferol or calcifediol from hospital admission to three months after discharge. Among the 140 older patients included (mean age 83±6.6, 57.8% females), 69 received cholecalciferol and 71 calcifediol. The mean plasma values of 25OH-Vitamin D3 found at the enrollment were 16.8 ± 9.9 ng/mL in patients receiving cholecalciferol and 18.8 ± 13.3 ng/mL in those treated with calcifediol (p =0.31). At the 3-month follow up, the mean concentration of 25OH-Vitamin D3 was significantly higher in patients treated with calcifediol than in patients treated with cholecalciferol (respectively, 30.7 ± 8.4 vs 45.4 ± 9.8 ng/mL, p <0.001). Supplementation with cholecalciferol or calcifediol results in both cases effective in reaching optimal circulating values of 25OH-VitaminD3 in the older patients suffering from hypovitaminosis D. However, supplementation with calcifediol led to average circulating values of 25OH- VitaminD3 significantly higher (over 50%) than those obtained with cholecalciferol.