Objective To investigate the effects of cigarette smoking extracts(CSE) on prociferation of human ESCC cell lines(EC109 and EC9706),and to explore the mechanism of tumorigenesis in human ESCC cell lines.Methods Two cell lines EC109 and EC9706 were cultured with CSE for different periods of time.Cells proliferation of ESCC was tested with MTT reduction assay.Genes expressions on COX-2 were detected by RT-PCR assays.Results The results of cell culture indicated that there was a time dependent manner for the cell proliferation with CSE on human ESCC cell lines EC109 and EC9706.The difference between groups was significant stacitically(P<0.01).The effects of cigarette smoking ethanol extracts(EE) on cell proliferation were correlated with the upgrade of COX-2 gene.Conclusion CSE could stimulate the proliferation of human ESCC cell lines EC109 and EC9706,and COX-2 expression upgrade may be one of causes for ESCC cell line EC109 proliferation treated with EE.