Objective: To study inhibitory effects of transcription factor activator protein-2α (Ap-2α) on proliferation of colon cancer cells in vitro and its mechanism. Methods: The pcDNA3.1 (+)-AP-2α recombinant plasmid was constructed. Plasmid pcDNA3.1 (+) AP-2α and pcDNA3.1 (+) were transfected into SW480 cells by liposome mediation. Normal SW480 cells were cultured as a negative control. The DNA-binding activity of AP-2α expressed in the SW480 cells of each group was analyzed by electrophoretic mobility shift Assay (EMSA). Proliferative activities of SW480 cells were evaluated by MTT assay at 24, 48 or 72 h after AP-2α transfection. The cell cycle was analyzed by flow cytometry at 48 h after transfection. The intracellular expression of p21/WAF1 was detected by Western blotting. Results: RT-PCR analysis showed the mRNA and protein levels of AP-2α significantly increased at 48 h after transfection of pcDNA3.1 (+)-AP-2α recombinant plasmid. The expressed AP-2α had higher DNA-binding activity. MTT assay indicated that the proliferation of SW480 cells was slowed down after transfection of pcDNA3.1 (+)-AP-2α recombinant plasmid. Cell cycle analysis demonstrated that the transfection of AP-2α gene increased the percentage of cells at G/G phase compared with normal cells (P <0.05). The expression of p21/WAF1 in SW480 cells increased at 48 h after AP-2α gene transfection. Conclusion. Overexpression of AP-2α inhibited the proliferation of SW480 cells in vitro, which is probably related with activation of p21/ WAF1.