Thermal decomposition kinetics of diglycidyl ether of bisphenol A(DGEBA)/4,4'-methylene dianiline(MDA)/neopenthy glycol(NPG) system were analyzed by thermogravimetry(TG). The values of activation energy and pre-exponential factor were calculated by Kissinger equation and these values were introduced to Arrhenius equation to get decomposition rate constants. Tlle constants were 3.16×10¹², 6.64×10¹³, 3.66×10¹⁴ and 2.83×10¹⁵15 sec^-1-1 for the System with 5. 10, 15, and 20phr of NPG, respectively.