Poly(L-lactic acid) (PLA)-degrading Pseudomonas sp. strain DS04-T was isolated from an activated sludge sample. A novel PLA depolymerase with a molecular weight of 34 kDa was purified to homogeneity from the culture supernatant of strain DS04-T. The optimum pH and temperature of the PLA depolymerase are 8.5 and 50 degrees C, respectively. The PLA depolymerase can also degrade triolein, poly(beta-hydroxybutyrate), and poly(epsilon-caprolactone). Na+ and K+ enhance the enzyme activity, whereas Zn2+, Mg2+, Cu2+, and Fe2+ inhibit it. The inhibition effect of different chemicals on the PLA depolymerase activity were examined, in which ethylenediaminetetraacetic acid was found to have a significant inhibitory effect. The main degradation product of the depolymerase is identified as lactic acid monomer by mass spectrometric analysis. POLYM. ENG. SCI., 51:454-459, 2011. (C) 2010 Society of Plastics Engineers