Background: Breast cancer is the leading cause of cancer-related death in the world, and it is of great value to reveal the molecular mechanisms of breast cancer progression and develop new therapeutic targets. Methods: Transwell assay is used to analyze the migration and invasion of breast cancer cells. Real-time PCR and western blotting assay are applied to detect the expression levels of epithelial–mesenchymal transition markers and the key members of Wnt/β-catenin and PI3K/AKT signaling pathways. Results: Manganese-12 acetate (Mn12Ac) significantly inhibited the migration and invasion of MCF7 and MDA-MB-231 breast cancer cells. Western blotting assay further showed that Mn12Ac significantly upregulated E-cadherin, and downregulated N-cadherin and vimentin. We further found that Mn12Ac reduced the mRNA expressions of epithelial–mesenchymal transition-associated transcription factors snail, slug, twist1, and ZEB1 using real-time PCR assay. Importantly, we further found that Mn12Ac significantly reduced the Wnt1 and β-catenin protein expressions, and suppressed the phosphorylation of PI3K and AKT in MCF7 and MDA-MB-231 breast cancer cells. Very interestingly, we also showed that Mn12Ac decreased the mRNA and protein expressions of programmed cell death ligand 1. Conclusion: Taken together, our results suggested that Mn12Ac inhibited the migration, invasion, and epithelial–mesenchymal transition by regulating Wnt/β-catenin and PI3K/AKT signaling pathways in breast cancer. © 2018 The Authors. Thoracic Cancer published by China Lung Oncology Group and John Wiley & Sons Australia, Ltd