AIM:To elucidate the role of overexpressed polo-like kinase1 (PLK1) in hepatocellular carcinoma (HCC).METHODS: We prospectively collected clinicopathological,immunohistochemical and semi-quantitative reverse transcription-polymerase chain reaction (RTPCR) data from 135 HCC patients undergoing successful hepatectomy. The correlations between PLK1 a expression and clinicopathologic variables were analyzed by Mann-Whitney U test. Prognostic factors were identified by univariate and multivariate analyses.RESULTS: Immunohistochemical results showed overexpression of PLK1 was mainly found in tumor tissues compared with tumor-free tissue. A similar a result was obtained by semi-quantitative RT-PCR. A total of 111 samples were positive for PLK1 a expression. The positive expression was correlated with venous invasion,tumor nodules and Edmondson grade. Furthermore, 1,3, 5-year survival rates in the positive expression group were significantly lower than the negative control group.Multivariate analysis showed that positive PLK1 expression was an independent risk factor for HCC.CONCLUSION: PLK1 could be a potential biomarker for diagnosis and therapy for HCC.