Chlorophyll(ide) b reductase (), chlorophyll b reductase, Chl b reductase) is an enzyme with systematic name 7<sup>1</sup>-hydroxychlorophyllide-a:NAD(P)<sup>+</sup> oxidoreductase. This enzyme catalyses the following chemical reaction
This enzyme carries out the first step in the conversion of chlorophyll b to chlorophyll a. It is involved in chlorophyll degradation, which occurs during leaf senescence, and it also forms part of the chlorophyll cycle, which interconverts chlorophyll a and b in response to changing light conditions.