Galectin-3 is known to modulate cell proliferation and apoptosis and is highly expressed in human cancers, but its function in gastric cancer is still controversial. Here, we examined the role of galectin-3 in gastric cancer cells by silencing it with synthetic double-stranded siRNA. After silencing of galectin-3, cell numbers decreased and cell shape changed. Galectin-3 siRNA treatment also induced G(1) arrest. DNA microarray analysis was used to assess changes in gene expression following galectin-3 silencing. We found that silencing of galectin-3 caused changes in gene expression. RT-PCR and real-time PCR were utilized for validation of the changes found in microarray studies. Western blot analysis confirmed changes in the expression of proteins of interest: cyclin D1, survivin, XIAP, XAF, PUMA, and GADD45alpha. Generally, it tended to increase the expression of several pro-apoptotic genes, and to decrease the expression of cell cycle progressive genes. We also confirmed that changes in the expression of these genes were caused by galectin-3 overexpression. Finally, we demonstrated that silencing of galectin-3 enhanced apoptosis induction with chemotherapeutic agents by further reducing the expression of anti-apoptotic and/or cell survival molecules such as survivin, cyclin D1, and XIAP, and increasing the expression of pro-apoptotic XAF-1. We conclude that galectin-3 is involved in cancer progression and malignancy by modulating the expression of several relevant genes, and inhibition of galectin-3 may be an approach to improve chemotherapy of gastric cancers.