MicroRNAs (miRNAs) are small, noncoding RNAs that can act as oncogenes or tumor suppressors in human cancer. Our previous study showed that miR-125b was a prognostic indicator for patients with hepatocellular carcinoma (HCC), but its functions and exact mechanisms in hepatic carcinogenesis are still unknown. Here we demonstrate that miR-125b suppressed HCC cell growth in vitro and in vivo . Moreover, miR-125b increased p21Cip1/Waf1 expression and arrested cell cycle at G1 to S transition. In addition, miR-125b inhibited HCC cell migration and invasion. Further studies revealed that LIN28B was a downstream target of miR-125b in HCC cells as miR-125b bound directly to the 3′ untranslated region of LIN28B , thus reducing both the messenger RNA and protein levels of LIN28B . Silencing of LIN28B recapitulated the effects of miR-125b overexpression, whereas enforced expression of LIN28B reversed the suppressive effects of miR-125b. Conclusion: These findings indicate that miR-125b exerts tumor-suppressive effects in hepatic carcinogenesis through the suppression of oncogene LIN28B expression and suggest a therapeutic application of miR-125b in HCC. (Hepatology 2010)