Considerable research has been conducted concerning galectin-9 and carcinomas, but little information is available about any relation with the hepatocellular carcinoma. In this study, we employed a small interfering RNA (siRNA) targeting galectin-9 to down-regulate the expression in HepG2 cells. As a result, after galectin-9 expression was reduced, cell aggregation was suppressed, while other behaviour such as the proliferation, adhesion and invasion to ECM, cell-endothelial adhesion and transendothelial invasion of the cells were markedly enhanced. When tumors of 200 patients with hepatocellular carcinoma were tested for galectin-9 expression by immunohistochemistry, binding levels demonstrated intimate correlations with the histopathologic grade, lymph node metastasis, vascular invasion and intrahepatic metastasis (P<0.05). Moreover, survival analysis indicated that patients with galectin-9 expression had much longer survival time than those with negative lesions, and the Log-rank test indicated that this difference was statistical significant (P<0.0001). The Cox proportional hazards model suggested that negative galectin-9 expression in hepatocellular carcinoma represented a significant risk factor for patient survival. We propose that galectin-9 might be a new prognostic factor with antimetastatic potential in patients with hepatocellular carcinoma.