The activity of icarrin (a flavonoid from Herba epimedii) was investigated in the regulation of bone remodeling, a process coupled by osteoblast-mediated bone forming and osteoclast-mediated bone resorption. By directly co-culturing mouse bone marrow stromal cells and mouse preosteoclastic RAW264.7, and transwell co-culturing rat ovarian follicular granulosa cells (FGC), a 30 % increase in alkaline phosphatase (ALP) activity and 25 % increase in estradiol level occurred. Compared with the antiresorptive drug, alendronate, and an anabolic drug, PTH1-34, icarrin possessed all of the positive effects on the co-culture by increasing ALP activity, estradiol production and decreasing tartrate-resistant acid phosphatase activity. A similar action of icarrin occurred on co-culture of mesenchymal stem cells, mouse peripheral blood mononuclear cells, and FGC. Overall, by using a co-cultured cell-based in vitro screening assay, icarrin is suggested as a new class of dual-action therapeutic agent for osteoporosis.