Objective：To investigate the effects of cancerous inhibitor of protein phosphatase 2A（CIP2A） expression on proliferation of laryngeal squamous cell carcinomas cells Hep-2 and its mechanism. Methods：siRNA-mediated CIP2A and negative control sequences were performed in Hep-2 cells. The experiment was designed into CIP2A siRNA group and control siRNA group. Colony formation assay was used to examine the role of CIP2A in cell proliferation. The impact of CIP2A on cell growth and cisplatin sensitivity was evaluated using MTT assay. Flow cytometry was used to examine cell cycle distribution and apoptotic rate. Quantitative real-time PCR and Western blot were applied to assess the expression of CIP2A，c-myc，AKT，p-AKT，and cyclinD1. Results：CIP2A knockdown in Hep-2 cells markedly decreased both CIP2A mRNA and protein expression，reduced the proliferation speed and colony formation（P=0.010） and increased the drug sensitivity of the cells to cisplatin（P=0.001）. In addition，CIP2A depletion blocked cell cycle at G1 phase（P=0.026） and decreased the percentage of S stage cells（P=0.007），and did not significantly alter cell apoptosis rate（P=0.216）. Western blot showed that CIP2A depletion downregulated CyclinD1，c-myc，p-AKT expression（P=0.011，P=0.011，P=0.010），but had no effects on the expression of total AKT protein（P=0.962）. Conclusion：CIP2A depletion inhibits cell proliferation and increases the sensitivity to cisplatin，mechanism of which may be related with decreased c-myc，p-AKT，and cyclinD1.