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Bone mesenchymal stem cells (BMSCs) are able to differentiate into multi types of lineages, so they have been widely applied in the stem cell transplantation. The BMSCs are usually needed to be expanded before transplantation due to their limited content in bone marrow. It has recently been reported that Icariin (ICA), a major constituent of flavonoids from the Chinese medical herb Epimedium brevicornum Maxim, promotes the proliferation of various types of differentiated cells. However, whether ICA can enhance BMSCs proliferation and the possible underlying mechanisms are still unknown. After being isolated and purified from rat bone marrow, cultured BMSCs are stimulated with different concentrations of ICA. The cytotoxicity of ICA is evaluated by the Cell Counting Kit-8 (CCK-8) assay method and the ICA optimal concentration for BMSCs proliferation is determined at 320 μg/L. Our work reveals that ICA induces an obvious phosphorylation of ERK and p38 kinases in BMSCs, no matter serum exists or not. Inhibition of ERK or p38 MAPK signaling by their specific inhibitors PD98059 or SP600125, respectively, not only prevents the activation of these kinases, but also attenuates cell proliferation induced by ICA. Furthermore, the downstream transcription factors of MAPK pathway, Elk1, Stat3, c-Myc and Fos, are also monitored by RT-PCR, and our results show that among them, Elk1 and c-Myc are significantly upregulated after ICA treatment. Taken together, our results demonstrate that ICA promotes the proliferation of rat BMSCs through activating ERK and p38 MAPK signaling which further leads to upregulation of their downstream transcription factors Elk1 and c-Myc. Our work provides a novel effective way to expand the content of BMSCs in vitro, which casts light on clinical applications of stem cell transplantation in the future.