Abstract Altered glycosylation is a hallmark of cancer. The core 1 β1,3-galactosyltransferase (C1GALT1) controls the formation of mucin-type O-glycans, far overlooked and underestimated in cancer. Here, we report that C1GALT1 mRNA and protein are frequently overexpressed in hepatocellular carcinoma tumors compared with nontumor liver tissues, where it correlates with advanced tumor stage, metastasis, and poor survival. Enforced expression of C1GALT1 was sufficient to enhance cell proliferation, whereas RNA interference–mediated silencing of C1GALT1 was sufficient to suppress cell proliferation in vitro and in vivo. Notably, C1GALT1 attenuation also suppressed hepatocyte growth factor (HGF)–mediated phosphorylation of the MET kinase in hepatocellular carcinoma cells, whereas enforced expression of C1GALT1 enhanced MET phosphorylation. MET blockade with PHA665752 inhibited C1GALT1-enhanced cell viability. In support of these results, we found that the expression level of phospho-MET and C1GALT1 were associated in primary hepatocellular carcinoma tissues. Mechanistic investigations showed that MET was decorated with O-glycans, as revealed by binding to Vicia villosa agglutinin and peanut agglutinin. Moreover, C1GALT1 modified the O-glycosylation of MET, enhancing its HGF-induced dimerization and activation. Together, our results indicate that C1GALT1 overexpression in hepatocellular carcinoma activates HGF signaling via modulation of MET O-glycosylation and dimerization, providing new insights into how O-glycosylation drives hepatocellular carcinoma pathogenesis. Cancer Res; 73(17); 5580–90. ©2013 AACR.