To investigate the effects of PDCD4 on apoptosis and the cell cycle in HCC cells, we detected the expression levels of Cyclin D1, CDK4, Cyclin E, P16 and apoptosis markers such as cleaved caspase 3, caspase 8, caspase 9, poly ADP ribose polymerase (PARP) in HepG2 and Huh7 cells with upregulation or downregulation of PDCD4. The gene discussed is CDK4; the disease is hepatocellular carcinoma.