Background: HAIR follicle stem CELLs (HFSCs) located in the bulge area has shown to be highly proliferative and could differentiate into neurons, glia, smooth muscle CELL, and melanocytes in vitro. Simvastatin is an HMG-CoA reductase inhibitor that exerts pleiotropic effects beyond simple low-density lipoprotein lowering and has a similar impact on the differentiation of bone marrow stromal CELLs and peripheral blood mononuclear CELLs. The present study examined the hypothesis that the application of simvastatin would induce the HFSCs differentiation into keratinocyte. Methods: The bulge of the HAIR follicle was anatomized, and HFSCs were cultivated. The flow cytometry and immunocytochemical staining for detection of nestin, CD34, and Kr15 biomarkers were performed before differentiation. In order to hasten the HFSCs differentiation to keratinocyte, HFSCs were treated with 1 μ M, 2 μ M, and 5 μ M of simvastatin daily for a week. After differentiation, the flow cytometry and immunocytochemical staining were performed with Kr15 and Kr10 biomarkers, and the MTT assay was carried out as an index of CELL viability and CELL growth. Results: Our results showed that bulge of HFSCs were nestin and CD34 positive and Kr15 negative. Simvastatin significantly increased the viability of HFSCs (p < 0. 05) at the concentration of 5 μ M. In addition, the percentages of keratinocyte-differentiated CELLs treated with 5 μ M of simvastatin showed a significant increase compared to all other treated groups (p < 0. 05). Conclusion: Our findings demonstrate that 5 μ M of simvastatin could induce HFSCs differentiation into keratinocyte.