In enzymology, a dihydrouracil oxidase (EC 1.3.3.7) is an enzyme that catalyzes the chemical reaction

5,6-dihydrouracil + O₂ ${\displaystyle \rightleftharpoons }$ uracil + H₂O₂

Thus, the two substrates of this enzyme are 5,6-dihydrouracil and O₂, whereas its two products are uracil and H₂O₂.

This enzyme belongs to the family of oxidoreductases, specifically those acting on the CH-CH group of donor with oxygen as acceptor. The systematic name of this enzyme class is 5,6-dihydrouracil:oxygen oxidoreductase. It employs one cofactor, FMN.