ACAT1 (acetyl-CoA acetyltransferase 1) is a mitochondrial enzyme that plays crucial roles in fatty acid metabolism and cholesterol homeostasis. Primarily, ACAT1 catalyzes the final step of mitochondrial beta-oxidation, cleaving medium- to long-chain 3-oxoacyl-CoAs into acetyl-CoA and shortened fatty acyl-CoA molecules 1. The enzyme functions reversibly, also catalyzing the condensation of acetyl-CoA molecules into acetoacetyl-CoA, making it essential for ketone body metabolism 1. Beyond its metabolic role, ACAT1 serves as a cholesterol esterification enzyme that converts free cholesterol to cholesteryl esters, particularly important in foam cell formation during atherosclerosis 1. Recent studies reveal ACAT1's function as a protein acetyltransferase, acetylating substrates like GNPAT to stabilize FASN and promote lipid metabolism in hepatocellular carcinoma 2, and acetylating ME1 to enhance lipogenesis in colorectal cancer 3. Clinically, ACAT1 inhibition shows therapeutic potential in cancer immunotherapy by enhancing CD8+ T cell function through increased plasma membrane cholesterol 4, and ACAT1 expression is associated with obsessive-compulsive disorder risk 5. The enzyme represents a promising target for treating metabolic disorders, atherosclerosis, and cancer.