Purpose To evaluate the expression of miR-21 in the tissues and cell lines of hepatocellular carcinoma,and to try to find its possible target genes.Methods The expression profile of miR-21 was detected in hepatocellular carcinoma tissues and cell lines.Mter miR-21 inhibitor was used,the alterations in the vitality and invasion of hepatocellular carcinoma cells were observed.The possible target gene of miR-21 was predicted by bioinformatics analysis.The influence of miR-21 inhibitors on the target gene activity was evaluated by dual luciferase reporting gene system.Results The expression level of miR-21 was significantly higher in hepatocellular carcinoma tissues than that in the adjacent ones (P ＜0.05).The expression level of miR-21 in hepatocellular carcinoma cells was significantly higher than that in the hepatic cells (P ＜0.01).After inhibiting miR-21,the viability and invasion ability of hepatocellular carcinoma cells were decreased (P ＜ 0.01).The expression level of programmed cell death 4 (PDCD4) in hepatocellular carcinoma tissues was significantly lower than that in the adjacent tissues (P ＜ 0.01).Its expression level in hepatocellular carcinoma cells was significantly lower than that in the hepatic cells (P ＜ 0.01).After interfering with PDCD4,the vitality and invasion ability of liver cancer cells were increased (P ＜ 0.05).Dual luciferase reporter gene assay indicated that by inhibiting miR-21,the expression level of PDCD4 was up-regulated (P ＜ 0.01).The vitality and invasion ability of liver cancer cells were reduced (P ＜ 0.001).Conclusion MiR-21 can regulate the growth and invasion of liver cancer cells through targeting PDCD4.