A new polymer, poly(imino isophthaloyl imino (2,4,8,10-tetraoksoaspiro [5,5] undekan-3,9-dipropylene)) [poly(IPIT)] was synthesized by an interfacial polycondensation reaction. The characterization of poly( IPIT) was conducted by using FT-IR, C-13-NMR, TG and DTA techniques. The kinetics of the thermal degradation of poly( IPIT) was investigated by thermogravimetric analysis at different heating rates. TG curves showed that the thermal decomposition of poly( IPIT) occurred in three stages. The apparent activation energies of thermal decomposition for poly( IPIT), as determined by the Tang method (TM), the Flynn-Wall-Ozawa method (FWO) and the Kissinger-Akahira-Sunose method (KAS) are 58.09, 57.7 and 61.0 kJ/mol for the first stage decomposition, 106.1, 105.6 and 109.8 kJ/mol for the second stage decomposition, and 138.1, 137.5 and 141.4 kJ/mol for the third stage decomposition, respectively.