Abstract: New special engineering thermoplastics poly (phthalazinone ether sulfone) (PPES) and poly (phthalazinone ether sulfone ketone) ［PPESK(1/1)］ containing phthalazinone were synthesized by step-polymerization. The kinetics of thermal degradation of PPES and PPESK(1/1) in nitrogen were studied at several heating rates by thermogravimetry analysis (TGA). According to the Satava method, the thermal degradation mechanism of PPESK(1/1) was randomly nucleating and nucleus growth, and the order of reaction n=1.The thermal degradation mechanism of PPES, however, was phase boundary controlled reaction and the order of reaction n=2.The kinetic parameters, including the energy of activation and frequency factor of degradation reaction for PPES and PPESK(1/1) were analyzed by the Friedman, Kissinger-Akahira-Sunose(KAS) and Ozawa methods. The aim of this work was to study the effects of heating rate and the ratio of ketone/sulfone on thermal degradation and life estimation. On the basis of kinetic parameters, the lifetime for high temperature was calculated and the ‘Kinetic Compensation Effects’(KCE) in the thermal degradation process was analyzed.