We report here the investigations on the thermal and thermo-oxidative degradation kinetics of a miscible high performance polymer blend poly(ether ether ketone)/poly(ether imide) (PEEK/PEI) with various compositions, measured in argon and air medium respectively The derivative thermogravimetric results indicate two-stage decomposition for both thermal and thermo-oxidative degradation for the entire composition of PEEK/PEI blend Interestingly the PEI addition is found to enhance the thermo-oxidation rate of PEEK The effective activation energy (E) as a function of conversion (a) is found for both the processes using model-free kinetics The model-free kinetics results reveal that the blend with 50% PEI content show high E value and the differential scanning calorimetry results corroboratively show a significant change in crystallinity for this PEI composition Based on these results the blend with composition 50/50 (PEEK/PEI) is suggested to have optimum thermal stability (C) 2010 Elsevier B V All rights reserved