Abstract: g author: ZHANG Jin, E-mail: davidz9132002 @yahoo. com Third Department of Breast Cancer, Cancer Institute and Hospital of Tianjin Medical University, Tianjin 300060, China Grant support: The Key Program of Frontier Technology and Foundamentals of Its Application in Tianjin (08jczdjc 23800 ) Absract Objective:To evaluate the efficacy of zoledronic acid in preventing bone loss induced by aromatase inhibitor in postmenopausal women with breast cancer. Methods:A total of63postmenopausal breast cancer patients were recruit-ed in the clinical trial. The zoledronic acid plus aromatase inhinitor group included 31postmenopausal breast cancer pa-tients. There were 32patients in the aromatase inhibitor group (the control group). The lumbar spine bone mineral density (LS BMD) and the incidence of osteopenia and osteoporosis were compared between the two groups at different time points. Results: After6 months, the zoledronic acid group had a higher LS BMD than the control group, but the difference between them was not significant ( P=0.099 ). There was no significant difference in the incidence of osteopenia and osteo-prosis between the two groups (osteopenia: P=0.124 ; osteoporosis: P=0.573 ). At 12months after treatment, the zoledronic acid plus aromatase inhinitor group had higher LS BMD than the control group ( P=0.008 ); and the incidence of osteopenia and osteoporosis in the zoledronic acid plus aromatase inhinitor group was lower than that in the control group (osteope-nia: P=0.048 ; osteoporosis: P=0.042 ). At 24months after treatment, the LS BMD in the zoledronic acid group was higher than that in the control group ( P=0.000 ); and the incidence of osteopenia and osteoporosis in the zoledronic acid plus aro-matase inhinitor group was lower than that in the control group (osteopenia: P=0.027 ; osteoporosis: P=0.011 ). The inci -dence of adverse effects between the two groups was similar except for bone pain. Patients in the zoledronic acid plus aro-matase inhinitor group had a higher rate of bone pain (P=0.037 ). Conclusion:Zoledronic acid is effective for preventing bone loss induced by aromatase inhibitor in postmenopausal breast cancer patients, with slight adverse reactions.