Objective：To investigate the effect of down-regulating PTEN on cell cycle in HeLa cells and to explore its underlying mechanism. Methods：PTEN-specific short hairpin RNA（shRNA）was synthesized and introduced into HeLa cells via lentivirus. The mRNA and protein expression of PTEN and Cyclin B1 were detected by qPCR and Western blot assay，respectively. Cell cycle distribution was determined by flow cytometry. Cyclin B1 protein expression was examined by Western blot after proteasome inhibitor MG-132 treatment to evaluate its protein stability. Results：Compared to the control group，both mRNA and protein levels of PTEN were decreased in HeLa cells transfected with PTEN-specific shRNA. PTEN down-regulation in HeLa cells induced cell cycle arrest in G2/M phase，decreased Cyclin B1 protein level，but had no effect on Cyclin B1 mRNA level. After MG-132 treatment，the expression of Cyclin B1 protein in the PTEN interference group was significantly elevated. Conclusion：Inhibition of PTEN expression in HeLa cells led to cell cycle arrest in G2/M phase，which could be caused by decreased expression level of cell cycle related proteins（Cyclin B1）.