Icariin, the main active flavonoid glucoside isolated from Herba epimedii, has been demonstrated to be a potential alternative therapy to prevent postmenopausal osteoporosis. Icariin has also been shown to regulate the proliferation and osteogenic differentiation of rat bone marrow stromal cells (rBMSCs). However, the detailed molecular mechanism of icariin has remained largely unknown. Besides, no investigation has focused on the relevance of icariin in the regulation of rat adipose-derived stem cells (rASCs) proliferation and osteogenic differentiation. In the present study, we detected that icariin promotes proliferation and osteogenic differentiation of rASCs in a concentration range from 10 ⁻⁸ M to 10 ⁻⁶ M, with 10 ⁻⁷ M to be the optimal concentration. We found that 10 ⁻⁷ M icariin significantly increased active RhoA protein expression and ROCK substrate molecule p-MYPT1 expression in rASCs. C3 (the RhoA inhibitor) treatment abrogated the increased proliferation and osteogenic differentiation of rASCs induced by icariin. Interestingly, we also found that C3 abrogated the activation of TAZ induced by icariin. Depletion of TAZ by siRNA transfection significantly blocked icariin promoted proliferation and osteogenic differentiation of rASCs. However, icariin induced active RhoA protein expression was not affected by TAZ specific siRNA transfection, suggesting that RhoA lies upstream of TAZ. Taken together, our data indicate that icariin promotes proliferation and osteogenic differentiation of rASCs by activating the RhoA-TAZ signaling pathway.