Mitofusin-2 (Mfn2) is a mitochondrial outer membrane protein involved in mitochondrial fusion. Its mutation can cause Charcot-Marie-Tooth disease. Recent studies of Mfn2 in cancer research have not included gastric cancer. We confirmed that Mfn2 expression was lower in tumor tissue than in normal gastric mucosal tissue and that it was negatively correlated with tumor size, indicating an anti-tumor role for Mfn2. In vitro experiments showed that Mfn2 overexpression suppressed gastric cancer cell proliferation and colony formation, weakened the invasion and migratory ability of cancer cells by downregulating MMP-2 and MMP-9, halted the cell cycle and induced apoptosis. Western blotting indicated the likely involvement of P21 and PI3K/Akt signaling. Therefore, Mfn2 is a potential anti-tumor gene and a potential therapeutic target for treating gastric cancer. The progress of gastric cancer may be delayed by controlling Mfn2 expression.