Aberrant expression of microRNAs (miRNAs) plays fundamental effect on the pathogenesis of hepatocellular carcinoma (HCC). MiR-27b was previously found to play important roles in human cancers. However, its expression status, clinical significance, and biological functions in HCC remain largely unclear. The expression status of miR-27b in HCC specimens and cells were determined with qRT-PCR. MTT, 5-bromodeoxyuridine (BrdU) proliferation assays, and flow cytometry analysis were carried out to assay proliferation, cell cycle, and apoptosis. A subcutaneous model was used to evaluated the HCC tumor growth in vivo. The putative target gene of miR-27b was disclosed by TargetScan and a luciferase reporter assay. The levels of miR-27b were overexpressed in HCC. Overexpression of miR-27b was correlated with adverse prognostic features and reduced survival rate. Inhibition of miR-27b in SMMC-7721 cells remarkably suppressed proliferative ability and cell-cycle progression while enhanced apoptosis. In contrast, miR-27b overexpression resulted in prominent increased proliferation and process of cell cycle and reduced apoptosis of Hep3B cells. In vivo studies showed that knockdown of miR-27b inhibited the in vivo growth of SMMC-7721 cells in mouse xenograft model. Furthermore, we confirmed that Fbxw7 was directly regulated by miR-27b and mediated the roles of miR-27b in HCC. We suggest that miR-27b serves as an oncogenic miRNA in HCC by modulating proliferation, cell-cycle progression, and apoptosis, and its oncogenic effect is mediated by its downstream target gene, Fbxw7.