Cyclin-dependent kinase inhibitor 3 (CDKN3) belongs to the protein phosphatases family and has a dual function in cell cycling. The function of this gene has been studied in several kinds of cancers, but its role in human hepatocellular carcinoma (HCC) remains to be elucidated. In this study, we found that CDKN3 was frequently overexpressed in both HCC cell lines and clinical samples, and this overexpression was correlated with poor tumor differentiation and advanced tumor stage. Functional studies showed that overexpression of CDKN3 could promote cell proliferation by stimulating G1-S transition but has no impact on cell apoptosis and invasion. Microarray-based co-expression analysis identified a total of 61 genes co-expressed with CDKN3, with most of them involved in cell proliferation, and BIRC5 was located at the center of CDKN3 co-expression network. These results suggest that CDKN3 acts as an oncogene in human hepatocellular carcinoma and antagonism of CDKN3 may be of interest for the treatment of HCC. (C) 2012 Elsevier Inc. All rights reserved.