Background: Breast cancer is one of the most common malignant tumors in women. However, the underlying molecular mechanisms of breast cancer are still far to clear. With the development of sequencing technology, we discovered that MAL2 is overexpressed in tumor tissues. But the major function of MAL2 in breast cancer has not to be well confirmed. Materials and methods: We downloaded and analyzed the MAL2 expression in The Cancer Genome Atlas (TCGA) database. Real-time quantitative polymerase chain reaction (RT-qPCR) was conducted to detect the expression of MAL2 in 35 breast cancer patients. Then, we performed proliferation, colony formation, migration, invasion and western blot assays to investigate the role of MAL2 in breast cancer cell lines (MDA-MB-231 and BT-549). Results: In our research, we found that MAL2 is remarkably overexpressed in breast cancer tissues compared to adjacent non-cancer tissues by RT-qPCR (T: N = 5.28 +/- 4.34:1.82 +/- 1.11, P < 0.001) and high expression of MAL2 has worse overall survival in TCGA cohort (P = 0.0032). Knocked down MAL2 could decrease the ability of proliferation, migration, and invasion of breast cancer cell lines. Our Western Blot assay results investigated that MAL2 could regulate EMT. Conclusion: In this study, we demonstrated the function of MAL2 in breast cancer cell lines and it might act as an oncogene in breast cancer. (C) 2018 Elsevier Inc. All rights reserved.