There has been no actual clinical report on the changes in bone turnover markers and bone mineral density (BMD) during ibandronate (IBN) treatment with or without vitamin D in Japanese postmenopausal osteoporotic patients. In this study, 48 treatment-naïve primary osteoporotic patients were divided into the IBN group or IBN with alfacalcidol (ALF) group. Bone turnover markers, 1,25(OH)2D3, and whole parathyroid hormone (PTH) were examined just prior to treatment and at 1, 4, 8, 12, 16, and 20 weeks of therapy. BMD was measured at 0 and 16 weeks. Values of TRACP-5b were significantly and continuously lower than baseline after 1 week of treatment in both groups. TRACP-5b values were significantly lower in the IBN group with ALF than in the IBN alone group at 4 and 8 weeks of treatment. Values of BAP were comparable between the groups at all-time points. Lumbar and hip BMD was slightly increased in both groups at 16 weeks of treatment, however, there was no significant difference between both groups. We witnessed a significant reduction in bone markers in both treatment groups, as well as an increase in 1,25(OH)2D3 and PTH in the IBN alone group.