The mitochondrial GTPase mitofusin-2 (Mfn2) gene is a novel gene characterized as a cell proliferation inhibitor. Mfn2 has previously been reported to play a role in regulating cell proliferation, apoptosis and differentiation in a number of cell types. However, there are no studies on the effect of Mfn2 in breast cancer. In this study, we aimed to elucidate the function and mechanism of Mfn2 in breast cancer. A plasmid encoding the complete Mfn2 open reading frame (pEGFP-Mfn2) was used to infect breast cancer cells. The effect of Mfn2 on proliferation was assessed by methyl thiazolyl tetrazolium and bromodeoxyuridine incorporation analyses. Flow cytometry, immunofluorescence and western blot analyses were used to test the effects of Mfn2 on cell cycle distribution and apoptosis. Additionally, the PI3K/Akt signaling pathway was analyzed after pEGFP-Mfn2 was transfected into MCF-7 cells. The results revealed that Mfn2 suppressed the proliferation of MCF-7 cells by regulating more cells at the G0/G1 phase and decreasing proliferating cell nuclear antigen and cyclin A expression. The results also demonstrated that the PI3K/Akt signaling pathway is involved in Mfn2-regulated proliferation and apoptosis. Taken together, this indicates that Mfn2 mediates MCF-7 cell proliferation and apoptosis via the PI3K/Akt signaling pathway. Mfn2 may thus be a significant therapeutic target in the treatment of breast cancer.