To investigate the effect of microRNA-221 (miR-221) on cell viability and apoptosis of hepatocellular carcinoma HepG2 cells. MiR-221 inhibitors and mimics were transfected into HepG2 cells. The expression of miR-221 was detected by real time quantitative RT-PCR. CellTiter-blue cell viability kit, Hoechst 33342/propidium iodide (PI) double staining assay, flow cytometry and Apo-ONE homogeneous caspase-3/7 kit were used to measure cell viability and apoptosis. MiR-221 inhibitors significantly inhibited the cell growth and miR-221 mimics increased cell viability 48 hours post-transfection measured by both CellTiter-blue cell viability kit and Hoechst 33342/PI assay (P is less than to 0.05). There was a positive correlation between these two assays (r = 0.993, P is less than to 0.01). With miR-221 mimics, the number of G1 stage cells (47.67%+/-1.53%) was significantly reduced as compared to the blank control (59.00%+/-1.00%) and the negative control (58.00%+/-1.00%, F = 81.77, P is less than to 0.01), and it was significantly raised in S stage (20.33%+/-1.15%) than in blank control (11.00%+/-1.00%) and negative control (12.00%+/-1.00%, F = 70.9, P is less than to 0.01) with flow cytometry analysis. More cell apoptosis and necrosis were significantly induced by miR-221 inhibitors 48 hours post-transfection detected by both Hoechst 33342/PI assay and flow cytometry PE Annexin V kit (P is less than to 0.05). The result from Apo-ONE homogeneous caspase-3/7 kit was consistent with the above two apoptotic assays, which showed that with miR-221 inhibitors, the activity of caspase-3/7 was significantly enhanced (P is less than to 0.05). MiR-221 contributes to the growth of hepatocellular carcinoma cells and miR-221 inhibition can induce cell apoptosis. miR-221 has the potential to become one of the new molecular targets for liver cancer therapy.