In this study, diethylene glycol terephthalate (DTP) and poly(ethylene terephthalate) (PET) fiber were degraded by crude enzymes extracted from a strain that was isolated from activated sludge obtained from factories. The feasibility of the biodegradation of the PET fiber is discussed through the rule of the biodegradation of DTP, which was used as the simulacrum of the biodegradation of the PET fiber. We concluded that the proper conditions for the degradation of DTP with the crude enzyme were 30 degrees C and a medium pH. Through the degradation kinetics, we determined that the crude enzyme was more capable of degrading DTP than was lipase. In addition, the crude enzyme also degraded the PET fibers. (c) 2006 Wiley Periodicals, Inc. I Appi Polym Sci 100: 3855-3859, 2006.