Drinking tea exhibits beneficial effects on bone health and may protect against osteoporosis, particularly in postmenopausal women. Theabrownin (TB) is the main component responsible for the biological activities of Pu-erh tea, but whether it possesses anti-osteoporotic potential remains unknown. Here we investigated the in vitro and in vivo anti-osteoporotic effects of TB in the RAW 264.7 cell line and ovariectomized (OVX) rats, respectively. Our in vitro studies showed that TB significantly suppressed RANKL-induced osteoclastogenesis and the expression of related marker proteins, including NFATc1, TRAP, c-Fos, and cathepsin K. In vivo studies showed that TB treatment effectively ameliorated blood biochemical parameters, organ weights and organ coefficients in OVX rats. In addition, TB treatment significantly improved femoral bone mineral density (BMD) and biomechanical properties. What’s more, TB treatment strikingly ameliorated bone microarchitecture in OVX rats because of increased cortical bone thickness and trabecular bone area in the femur. Our study therefore demonstrated that TB can inhibit RANKL-induced osteoclastogenesis in vitro and prevent bone loss in ovariectomized rats. Consequently, TB has a promising potential in postmenopausal osteoporosis treatment.