Objective To investigate effects of F-actin cytoskeleton on differentiation of endothelial progenitor cells (EPCs) under laminar shear stress. MethodsEPCs isolated from rat bone marrow were treated with laminar shear stress (1.2 Pa). Then the gene and protein expressions of the endothelial cell differentiation markers, such as vWF and CD31, were assayed with real time RT-PCR and Flow Cytometry. The effects of laminar shear stress on F-actin cytoskeleton and Ras activity were investigated by immunofluorescence technique and Pull-down assay. Results Compared with the untreated group, the expressions of vWF and CD31 were obviously increased in the group treated with laminar shear stress (P<0.05). Moreover, exposure of EPCs to laminar shear stress led to the reorganization of cytoskeleton and enhanced the activity of Ras in EPCs. The treatment to EPCs with either F-actin stabilizer jasplakinolide or depolymerizers cytochalasin D inhibited the cytoskeleton reorganization induced with laminar shear stress, the activity of Ras and the up-regulation of the vWF and CD31 genes. However, over-expression of Ras augmented the up-regulation of the vWF and CD31 genes induced by laminar shear stress in EPCs.Conclusions The mechanism that laminar shear stress accelerates the differentiation of EPCs may be related with the laminar shear stress-induced cytoskeleton rearrangement and Ras activation. This study is of significance in revealing the mechanism of vascular endothelial repair which could be useful for the prevention and treatment of atherosclerosis.