Pheophorbide a oxygenase (, pheide a monooxygenase, pheide a oxygenase, PAO) is an enzyme with systematic name pheophorbide-a,NADPH:oxygen oxidoreductase (biladiene-forming). This enzyme catalyses the following chemical reaction
Pheophorbide a oxygenase participates in chlorophyll degradation. Loss-of-function mutations in the gene can lead to a stay-green phenotype in plants.