Altered expression of family with sequence similarity 84, member B (FAM84B) has been found in various human cancers. However, the expression and function of FAM84B in pancreatic ductal adenocarcinoma (PDAC) has not been studied. Here, by analyzing The Cancer Genome Atlas cohort, we found that FAM84B amplification was observed in 11% of 141 PDAC patients, and FAM84B amplification was correlated with higher mRNA expression of FAM84B. FAM84B amplification and overexpression was significantly correlated with poor overall survival. Moreover, knockdown of FAM84B in PDAC cell lines suppressed cell proliferation and induced apoptosis. FAM84B knockdown also suppressed mitochondrial function and glycolysis of PDAC cells. Interestingly, knockdown of FAM84B decreased the nuclear accumulation of β-catenin, and the expression of c-Myc and lactate dehydrogenase A, but enhanced the expression of Survivin. On the contrary, FAM84B overexpression displayed reversed effects in cell proliferation, apoptosis, mitochondrial function, and glycolysis, which was blocked by the Wnt/β-catenin pathway inhibitor (XAV939). In addition, PDAC cells with lower expression of FAM84B were more sensitive to gemcitabine-induced cell proliferation inhibition both in vitro and in vivo. In conclusion, FAM84B plays an important role in aerobic glycolysis and tumorigenesis in PDAC and Wnt/β-catenin may be involved in this process.