Introduction In terms of the balance between benefits and risks of long-term treatment with bisphosphonate, uncertainties remain regarding the optimal treatment duration. We investigated effects of continuous long-term treatment for 10 years with bisphosphonate in postmenopausal osteoporosis patients. Materials and methods Fifty five patients in the outpatient clinic of our hospital have been continuously treated with alendronate or risedronate for 10 years. All data were retrospectively collected. The age, height, weight, total muscle volume, total fat volume, and BMD at the lumbar spine, total hip and distal 1/3 radius, alkaline phosphatase (ALP), urinary type I collagen cross-linked N-telopeptide (uNTX) and tartrate-resistant acid phosphatase-5b (TRAP5b), calcium (Ca) and phosphate (P) levels were measured pre- and after the start of 10-year continuous treatment. Results BMD at the lumbar spine increased continuously over the 10-year period, while BMD at the total hip slightly but significantly decreased, and that at the 1/3 radius did not show any significant change over the 10 years. Serum Ca value was significantly decreased after the start of treatment, and became stable within the reference range from the second year. Bone resorption markers such as uNTX and TRAP5b significantly decreased from the second year after the start of treatment and no significant changes were observed thereafter. There were no serious medical adverse events including atypical femoral fractures and osteonecrosis of the jaw. Conclusion We believe that the continuous use of alendronate and risedronate for 10 years could be an option for the treatment of postmenopausal osteoporosis patients.