These authors contributed equally to this work Purpose: Sodium selenite (Na 2 SeO 3 ) has been known to restore the antioxidant capacity of bone marrow mesenchymal stem cells (BMSCs), reduce the production of reactive oxygen species (ROS) in the cells, and promote cell proliferation and inhibit cell apoptosis. However, it is still not clear whether selenium can mediate the differentiation and inhibit the induced hemagglutination of BMSCs. In this study, we attempted to explore the effect of Na 2 SeO 3 on these aspects of BMSCs. Methods: We evaluated the fate of the MSCs isolated from the bone marrow of mice by studying their differentiation and proliferation after treatment with Na 2 SeO 3 . We also simultaneously evaluated the coagulation reaction induced by Na 2 SeO 3-treated BMSCs in vitro. Results: While the mice-derived BMSCs expressed CD44, CD73, CD90, and CD105, they did not express CD45. The morphology of the derived cells was homogeneously elongated. These results showed that the isolated cells are indeed BMSCs. We found that 0.1 μM and 1 μM of Na 2 SeO 3 promoted the proliferation and apoptosis of BMSCs, respectively. This showed that Na 2 SeO 3 can be toxic and exert certain side effects on the BMSCs. The results of the osteogenic and adipogenic assay showed that 0.1 μM Na 2 SeO 3 could significantly promote the osteogenic and adipogenic differentiation of BMSCs by upregulating the lipid factors (LPL and PPRAG) and osteogenic factors, RUNX2, COL1, and BGP, in a concentration-dependent manner. Coagulation experiments in animals (mice and rats) revealed that Na 2 SeO 3 can reduce the coagulation time of BMSCs in a concentration-dependent manner, which is related to the high expression of hematopoietic factors (SDF-1α, GM-CSF, IL-7, IL-8, IL-11, and SCF). Conclusion: Na 2 SeO 3 promotes the proliferation and differentiation as well as reduces the coagulation time of BMSCs, and this effect might enhance the therapeutic effect of BMSCs.