Gastric cancer (GC) is one of the most common cancers and lethal malignancies in the world. Discovering novel biomarkers that correlate with GC may provide opportunities to reduce the severity of GC. As one of Notch receptor family members in mammals, Notch4 plays an important role in carcinogenesis of several tumors. However, the precise function and mechanism of Notch4 in GC remain undefined. To address this question, we investigated whether Notch4 could be involved in GC progression. We found that Notch4 was activated by overexpressing exogenous intracellular domain of Notch4 (ICN4), and Notch4 activation promoted GC growth in vitro and in vivo, while Notch4 inhibition using ICN4 siRNA had opposite effects. In addition, Notch4 activation induced expression and activation of Wnt1, β-catenin and downstream target genes, c-Myc and cyclin D1, in GC cells, while Notch4 inhibition had opposite effects. Moreover, β-catenin depletion by siRNA attenuated cell proliferation induced by Notch4 activation. Therefore, our results revealed that Notch4 activates Wnt1/β-catenin signaling to regulate GC growth.