A new polyester containing diimine ring, poly(imino isophthaloyl imino (glyoxai bis(2-methyl-4-hydroxy phenyl)imin)) poly[IPIGI] was synthesized by an interfacial polycondensation reaction. The structure of poly[IPIGI] was confirmed by FT-IR and solid state C-13 NMR techniques. The thermal stability was tested by TG-DTA and solubility was also studied. The kinetics of the thermal degradation of poly[IPIGI] was investigated by thermogravimetric analysis at different heating rates. TG curves showed that the thermal decomposition or poly[IPIGI] occurred in two stages. The apparent activation energies of thermal decomposition for poly[IPIGI], as determined by the Tang method (TM), the Flynn-Wall-Ozawa method (FWD), the Kissenger-Akahira-Sunose method (KAS) and the Coats-Redfern method (CR) are 74.8, 75.2, 76.5 and 83.9 kJ mol(-1) for the first stage decomposition and 143.1, 143.7, 147.0 and 156.2 kJ mol(-1) for the second stage decomposition, respectively. The mechanisms of each stage decomposition were also investigated by master plots.