We determined the effect of risedronate on the trabecular microstructure of ovariectomized rat tibiae, using micro-computed tomography, in order to investigate how changes in microstructure contribute to biomechanical properties. Fifty 18-week-old rats underwent sham operation (n=10) or ovariectomy (OVX) (n=40). The OVX rats were further divided into four groups (n=10 for each group) and treated with risedronate at doses of 0, 0.1, 0.5 or 2.5 mg/kg for 9 months. OVX caused deterioration of three-dimensional trabecular microstructure, notably structure model index (SMI) and connectivity density, while treatment of OVX rats with risedronate at 0.5 and 2.5 mg/kg improved those deleterious microstructural changes. Biomechanical property, as assessed by finite element analysis (FEA), correlated significantly with trabecular bone volume fraction (BV/TV), and the correlation further increased substantially when microstructural parameters were added, especially SMI and connectivity density, with risedronate therapy. Thus, it is suggested that, in addition to increasing bone mass, risedronate improves biomechanical property by maintaining a plate-like structure as well as connectivity of trabeculae.