In enzymology, a leucoanthocyanidin reductase (EC 1.17.1.3) (LAR, aka leucocyanidin reductase or LCR) is an enzyme that catalyzes the chemical reaction

(2R,3S)-catechin + NADP⁺ + H₂O ${\displaystyle \rightleftharpoons }$ 2,3-trans-3,4-cis-leucocyanidin + NADPH + H⁺

The 3 substrates of this enzyme are (2R,3S)-catechin, NADP⁺, and H₂O, whereas its 3 products are 2,3-trans-3,4-cis-leucocyanidin, NADPH, and H⁺.

This enzyme belongs to the family of oxidoreductases, specifically those acting on CH or CH₂ groups with NAD⁺ or NADP⁺ as acceptor. The systematic name of this enzyme class is (2R,3S)-catechin:NADP⁺ 4-oxidoreductase. This enzyme is also called leucocyanidin reductase. This enzyme participates in flavonoid biosynthesis.

The enzyme can be found in the plant Hedysarum sulphurescens and in Vitis vinifera (grape).^[1]