The assigned glass-transition temperature, and the mechanism for the thermal decomposition of PETI/IM7 were obtained using DSC, DMA and TGA/FTIR/MS techniques. The assigned glass-transition temperature was shifted to a much higher temperature after the sample was cured. TG/MS/FTIR results indicated that water and NMP were released from the fresh sample during the staging step. NMP and CO2 were the major products released from the sample during the curing step. The possible three-step mechanism of decomposition, which was only based on the gas evolution, was proposed.