The results revealed that ZFAS1 expression was significantly downregulated in breast cancer cell lines when compared with the levels in controls. In vitro experiments also demonstrated that ZFAS1 overexpression significantly suppressed cell proliferation by causing cell cycle arrest and inducing apoptosis in breast cancer cells. Further functional assays indicated that ZFAS1 overexpression inhibited cell migration and invasion by regulating epithelial mesenchymal transition. These findings indicated that the lncRNA ZFAS1 may be a tumor suppressor in breast cancer, and thus, may serve as a potential therapeutic target for patients with breast cancer. ZFAS1 overexpression in MCF-7 and MDA-MB-231 cells resulted in significantly decreased clonogenic survival.