The thermal cure behavior of diglycidyl ether bisphenol-A/carboxylated polyester hybrid powder coating system in the absence and presence of catalyst was monitored using differential scanning calorimetry. Curing temperatures were between 160 and 200 °C. The experimental results showed an autocatalytic behavior of the reaction, which could be described by the model proposed by Kamal. This model includes two rate constants k1 and k2 and two reaction orders m and n. The activation energies Ea1 and Ea2 of these rate constants were 51.7 and 42.3 kJ/mol for uncatalyzed cure reaction and 40.6 and 35.0 kJ/mol for externally catalyzed reaction. The average order of the overall reaction was found to be 2.45 and 2.72 for uncatalyzed and catalyzed system, respectively. Except for the late stage of cure reaction, the model agreed well with the experimental data, especially at high temperatures and in externally catalyzed cure reaction. A diffusion factor was introduced into the model to account for the effect of diffusion on the cure rate. The modified model greatly improved the predicated data at the late stage of cure reaction.