A novel PHB depolymerase from a thermophilic Streptomyces sp. MG was purified to homogeneity by hydrophobic interaction chromatography and gel filtration. The molecular mass of the purified enzyme was 43 kDa as determined by size exclusion chromatography and 41 kDa by SDS-PAGE. The optimum pH and temperature were 8.5 and 60 degrees C respectively. The enzyme was stable at 50 degrees C and from pH 6.5-8.5. The enzyme hydrolyzed not only bacterial polyesters, i.e. poly(3-hydroxybutyric acid and poly(3-hydroxybutyrate-co-3-hydroxyvalerate), but also synthetic, aliphatic polyesters such as polypropiolactone, poly(ethylene adipate) and poly(ethylene succinate).