Due to their unique physicochemical properties, nanomaterials can optimize drug delivery and reshape the tumor microenvironment. Manganese-based nanomaterials are primarily used in tumor immunotherapy for the following purpose, including targeted activating of the cyclic GMP-AMP synthase-stimulator of interferon gene pathway to enhance immunogenicity, utilizating of manganese′s redox properties to regulate the tumor microenvironment, and developing of manganese-based magnetic resonance imaging contrast agents to monitor immune responses in real time. In this review, synthesis methods of manganese-based nanomaterials such as thermal decomposition method, hydrothermal/solvothermal synthesis method, and chemical precipitation/mixing method as well as an in-depth analysis of their applications in tumor immunotherapy including immune regulation, regulation of tumor microenvironment and enhanced magnetic resonance imaging were reviewed.