Monoamine oxidase A (MAOA) is a membrane-bound mitochondrial enzyme existing in almost all vertebrate tissues that catalyzes the degradation of biogenic and dietary -derived monoamines. MAOA regulates neurotransmitter metabolism and is associated with anti-tumor immune responses. Previous most studies focused on the role of MAOA in tumor cells, while more recent findings suggest that MAOA plays an equally significant role in tumor-associated immune cells. In this review, we summarize the regulatory effect of MAOA on inhibitory tumor microenvironment, and the suppression function on the activity of various types of tumor-associated immune cells (e.g., CD8+T cells and tumor-associated macrophages) by directly affecting monoamines. We propose that developing novel MAOA-inhibitor drugs and exploring multidrug-combination strategies may enhance the efficacy of immune governance. Thus, MAOA may act as a novel target for tumor immunity and influence the effect of tumor immunotherapy