In enzymology, a putrescine oxidase (EC 1.4.3.10) is an enzyme that catalyzes the chemical reaction

putrescine + O₂ + H₂O ${\displaystyle \rightleftharpoons }$ 4-aminobutanal + NH₃ + H₂O₂

The 3 substrates of this enzyme are putrescine, O₂, and H₂O, whereas its 3 products are 4-aminobutanal, NH₃, and H₂O₂.

This enzyme belongs to the family of oxidoreductases, specifically those acting on the CH-NH2 group of donors with oxygen as acceptor. The systematic name of this enzyme class is putrescine:oxygen oxidoreductase (deaminating). This enzyme participates in urea cycle and metabolism of amino groups. It employs one cofactor, FAD.