Background: Adjuvant therapy with aromatase inhibitors (AI) is associated with increased bone loss in postmenopausal women. We assessed changes in bone mineral density (BMD) from baseline to 60 months of treatment in patients receiving anastrozole (ANA) as initial adjuvant therapy with/without oral bisphosphonates (Bis). Methods: Postmenopausal women with endocrine responsive breast cancer receiving ANA as adjuvant therapy at our hospital since 2004 were enrolled in this study. BMD was assessed by dual-energy X-ray absorptiometry at baseline and after 6, 12, 24, 36, 48 and 60 months. Oral Bis (risedronate or alendronate) treatment was initiated when patients were diagnosed as having osteoporosis with a T-score of -2.5 or lower. Results: Fifty-seven patients were enrolled in the study between 2004 and 2011. Patients’ median age was 65 years (range 50~85) and the median follow-up period was 46.3 months (9.6~83.8). Thirty-five patients were administered Bis (risedronate in 27 patients, alendronate in 8 patients). Within 6 months of hormone therapy, BMD decreased by 0.3% from baseline at the lumbar spine and BMD decreased by 1.2% at the femoral neck. However, BMD increased by 2.8% at the lumbar spine and BMD decreased 0.5% at the femoral neck for 60 months of treatment. In patients treated with upfront Bis (n=24), 4.9% BMD increase from baseline was noted at the lumbar spine whereas in those without Bis (n=20) BMD decreased by 4.6% from baseline within 24 months (p=0.0002). Fractures were observed in 4 patients (7.0%), and 1 patient (1.8%) had fragility fracture. Conclusions: Oral Bis prevented ANA-induced bone loss, and upfront treatment of Bis significantly increased BMD at the lumber spine.