D-amino acid oxidase (DAO) is an FAD-dependent enzyme responsible for catalyzing the deamination and oxidation of D-amino acids, producing the corresponding α-keto acids and ammonia. DAO consists of multiple functional domains and is primarily located in the cytoplasm and peroxisomes. DAO plays a significant role in regulating the metabolism and clearance of D-amino acids, influencing cellular redox balance and neurotransmitter levels. The expression of DAO is tissue-specific, and mutations or dysregulation of its expression are associated with various diseases, including neurodegenerative diseases, psychiatric disorders, and kidney diseases. The activity of DAO is regulated by multiple factors, affecting the physiological and pathological processes of cells.