Abstract: Objective: To observe the influence of lipopolysaccharide（LPS） on the proliferation and cell cycle of normal human skin fibroblasts.Methods: Purified dermal fibroblasts were exposed to different concentrations of LPS（0.005-1.0μg/ml）from E.coli.Then cells were counted on a daily basis from day 1 to day 9 under inverted phase contrast microscope after the administration of LPS,and the cell cycle of fibroblasts at logarithmic stage at day 6 after LPS administration was assayed with flow cytometry.Results: The amount and the percentage of S phase cells in cell cycle of normal human skin fibroblasts increased when challenged with LPS at the concentrations of 0.005-0.1μg/ml,and the increase showed a concentration dependent manner.However,when the concentration of LPS was 0.5μg/ml,cell amounts and the percentage of S phase cells began to decrease,but still higher than the control group.When LPS concentration reached 1.0μg/ml,both cell amounts and percentage of S phase cells were lower than the control group.Conclusion: LPS promotes the proliferation of normal human skin fibroblasts within a certain range of low concentrations,while high concentration of LPS inhibits the proliferation of normal human skin fibroblasts.