Poly(3-hydroxybutyrate) depolymerase was purified to homogeneity from the culture filtrate of Paecilomyces lilacinus D218 by column chromatography on CM-Toyopearl 650M and hydroxylapatite. The molecular weight of the enzyme was estimated to be 48,000 by SDS-PAGE. Maximal activity was observed near pH 7.0 ans 45 degrees C. The K-m and V-max walues for PHB were 0.13 (mg/ml) and 3750 (U/mg protein), respectively. The enzyme hydrolyzed PHB and p-nitrophenyl fatty acids but not polycaprolactone and triglycerides.