Objectives: We investigated drug adherence of once yearly intravenous bisphosphonate in patients with osteoporosis or osteoporotic fractures, and factors that influence their adherence.Materials and Methods: Patients treated with once yearly intravenous bisphosphonate were asked about drug information and drug adherence using questionnaires. Factors related drug adherence were analyzed between non adherence group and adherence group.Results: 65 patients (49.6%) were adherence group, 66 patients (50.3%) were included in non-adherence group. In group 1, were administered mainly due to ‘after physicians suggestion’ in 22 cases (36.1%) and ‘for ease of administration’ in 17 cases (27.9%). In group 2, the patients were not readministered mainly due to economic reasons in 21 cases (42%), unconcerning to osteoporosis in 14 cases (28%).Conclusions: This study shows ‘doctor's suggestion’ and ‘ease of administration’ could enhance drug adherence.