In enzymology, an anthocyanidin reductase is an enzyme that catalyzes the chemical reaction The 3 substrates of this enzyme are flavan-3-ol, NAD+, and NADP+, whereas its 4 products are anthocyanidin, NADH, NADPH, and H+. This enzyme belongs to the family of oxidoreductases, specifically those acting on the CH-CH group of donor with NAD+ or NADP+ as acceptor. The systematic name of this enzyme class is flavan-3-ol:NAD(P)+ oxidoreductase. Other names in common use include AtANR, and MtANR. This enzyme participates in flavonoid biosynthesis.