Abstract: Aldehyde oxidase (AOX), a highly conserved molybdoflavoenzyme in mammal cytoplasm, has broad substrate specificity and ability to catalyze the oxidation of aldehydes and nitrogen, oxygen-containing heterocyclic rings. AOX was found to widely distribute with the individual differences in vivo and plays an important role in phase Ⅰ metabolism of drugs and xenobiotics. The biological characteristics of AOX and its contributions in drug metabolism are introduced briefly in this review.