Poly(propylene terephthalate) (PPT) was subjected to aging at high temperatures (150-190degreesC) in air and some mechanical (impact strength), physical (weight loss), and electrical (dc conductivity and ac electrical strength) properties were determined as a function of aging time and temperature. Some chemical-physical characteristics (such as the average molecular weight, the carboxyl end-group content, and crystallinity degree) were investigated during the degradation process, as well. From the collected data, the thermal endurance parameters (i.e., the temperature index and the halving interval), which are key parameters in the determination of materials reliability and design of electrical insulating system, were derived according to IEC 216 Standard, and compared with those relevant to other thermoplastic polyesters. (C) 2004 Wiley Periodicals, Inc.