Fatty acid synthase (FASN) is a key enzyme in fatty acid metabolism, playing a crucial role in energy storage and biofilm synthesis. Recent studies have highlighted its regulatory effects on immune cells and its implications in immune-related diseases. This review discusses the molecular mechanisms and functional roles of FASN in immune cell biology, including macrophages, T lymphocytes, and other immune cells. FASN influences the polarization, activation, and function of immune cells, contributing to various pathophysiological processes such as inflammation, tumor development, and autoimmune diseases. Additionally, FASN is involved in the pathogenesis of infectious diseases, autoimmune diseases, inflammatory bowel disease, diabetes, nonalcoholic fatty liver disease, and atherosclerosis. Targeting FASN has emerged as a promising therapeutic approach for these conditions, but further research is needed to clarify its specific mechanisms and optimize treatment strategies.Fatty acid synthase (FASN) is a key enzyme in fatty acid metabolism, playing a crucial role in energy storage and biofilm synthesis. Recent studies have highlighted its regulatory effects on immune cells and its implications in immune-related diseases. This review discusses the molecular mechanisms and functional roles of FASN in immune cell biology, including macrophages, T lymphocytes, and other immune cells. FASN influences the polarization, activation, and function of immune cells, contributing to various pathophysiological processes such as inflammation, tumor development, and autoimmune diseases. Additionally, FASN is involved in the pathogenesis of infectious diseases, autoimmune diseases, inflammatory bowel disease, diabetes, nonalcoholic fatty liver disease, and atherosclerosis. Targeting FASN has emerged as a promising therapeutic approach for these conditions, but further research is needed to clarify its specific mechanisms and optimize treatment strategies.