Two polyhydroxyalkanoate depolymerases, PHAase I and PHAase II, were purified to homogeneity from the culture supernatant of an effective PHA-degrading bacterium, Pseudomonas mendocina DS04-T. The molecular masses of PHAase I and PHAase II were determined by SDS-PAGE as 59.4 and 33.8 kDa, respectively. Their optimum pH values were 8.5 and 8, respectively. Enzymatic activity was optimal at 50 A degrees C. Both purified enzymes could degrade PHB, PHBV, and P(3HB-co-4HB). Addition of Na+ and K+ slightly increased the rate of PHAase II. EDTA significantly inhibited PHAase II but not PHAase I. Mercaptoethanol and H2O2 also inhibited the activities of both enzymes.