Objective:To observe the effects of lipopolysaccharides(LPS) of different concentrations on the proliferation of mesenchymal stem cells(MSCs). Methods:Mesenchymal stem cells(MSCs) were isolated from wild and TLR4 gene deletion mice respectively by method of differential adherence to plastic, and their phenotypical properties were analyzed in passage 3-6 by flowcytometer. Flowcytometry showed that MSCs were CD34-,CD45- and CD105+-CD29+-CD44+. MSCs isolated from wild mice were treated with LPS of different concentrations(0.1,1.0,5.0,10.0,20.0 -滋g/ml). MSCs proliferation was detected by CCK-8(Cell Count Kit-8) co-cultured method at 24 h and 48 h respectively. In addition, MSCs isolated from TLR4 gene deletion mice incorpted with LPS 1.0 -滋g/ml were used to explore the possible mechanism of promoting MSCs proliferation. Results:Low dose LPS(0.1~5.0 -滋g/ml) strikingly improved the proliferation of MSCs in vitro(P < 0.05). The stimulation with LPS 5.0 -滋g/ml reached maximum effects on MSCs proliferation. While the concentration of LPS was further increased more than 5.0 -滋g/ml, the improvement effects on MSCs proliferation showed a tendency to decline, but the effect at 20.0 -滋g/ml was still greater than those in control group(P > 0.05). There was no significant effects on the proliferation of MSCs isolated from TLR4 gene deletion mice induced by LPS. Conclusion:The present study revealed that LPS could improve the proliferation of MSCs through TLR4, and the mechanism might activate the Toll -like receptor4 pathway