Detailed kinetic studies of polyisoimide based upon 4,4`-oxydianiline (ODA) and 4,4`-oxy-diphthalic anhydride (ODPA) were performed by both isothermal and dynamic differential scanning calorimetric measurements. The polyisoimide system exhibited a limited degree of cure as a function of isothermal temperature because of the diffusion-controlled reaction rates. The kinetic parameters were determined from both isothermal and dynamic experimental data. The thermal imidization of polyisoimide was well described by first order kinetics with an activation energy of 170~180 kJ/mol. The activation energy obtained from isothermal experiments was similar to the values obtained from dynamic experiments utilizing Kissingers`s and Flynn/wall`s methods.