Cigarette smoking is intimately related with the development of chronic obstructive pulmonary diseases, and alveolar epithelium is a major target for the exposure of cigarette smoke ex- tract. In order to investigate the effect of cigarette smoke extract on the proliferation of alveolar epithelial cell type Ⅱand its relationship with P21WAF1, the alveolar epithelial type Ⅱ cell line (A549) cells were chosen as surrogate cells to represent alveolar epithelial type Ⅱ cells. MTT assay was used to detect cell viability after interfered with different concentrations of cigarette smoke ex-tract. It was observed cigarette smoke extract inhibited the growth of A549 cells in a dose- and time-dependent manner. The morphological changes, involving the condensation and margination of nuclear chromatin, even karyorrhexis, were observed by both Hoechst staining and electronic mi-croscopy. Flow cytometry analysis demonstrated the increased cell percentages in G1 and subG1phases after the cells were incubated with cigarette smoke extract. The expression of p21WAF1 protein and mRNA was also significantly increased as detected by the methods of West blot or reverse transcription-polymerase chain reaction respectively. In conclusion, cigarette smoke extract inhibits the proliferation of alveolar epithelial cell type Ⅱ and blocks them in G1/S phase. The intracellular accumulation of P21WAF1 may be one of the mechanisms which contribute to cigarette smoke ex-tract-induced inhibition of cell proliferation.