Androgens are targeted as a potential treatment for osteoporosis because of their anabolic effects;​ however, their specific role in bone growth and maintenance is unclear. We manipulated androgen receptors (ARs) to study specific androgen effects on bone without increasing circulating concentrations. This study used AR overexpression, targeted to mature osteoblasts using a 2.3-kb type I collagen promoter coupled to a rat AR gene sequence, to investigate the role of AR transactivation in bone. High-resolution micro-computed tomography showed no differences in total cross-sectional area. Cortical bone width and area were reduced with increased marrow cavity in male AR2.3-transgenic mice. These mice also showed reductions in stiffness, maximum load, post-yield deflection and work-to-failure. Dynamic histomorphometric analysis at 8 weeks showed increased periosteal, but decreased endosteal labeling with decreased periosteal and increased endosteal resorption. These results indicate that the effects of androgens differ at each surface, and are inhibitory rather than anabolic in mature bone.