The cure rate of diglycidyl ether of bisphenol A (DGEBA)/4,4'-methylene dianiline (MDA) system with or without MDA-endcapped carboxyl-terminated butadiene acrylonitrile (CTBN) rubber was studied by autocatalytic cure rate expression. All the cumulative conversion curves for DGEBA/MDA system with or without MDA-endcapped CTBN (20 phr) showed s-shape and this meant that the two systems followed the typical autocatalytic reaction. The cure rate of the system with MDA-endcapped CTBN (20 phr) was faster than that of the system without MDA-endcapped CTBN (20 phr). The activation energies of k(1) and k(2) for DGEBA/MDA system were 54.01 kJ/mol and 44.06 kJ/mol, respectively and those of k(1) and k(2) for the system with MDA-endcapped CTBN (20 phr) were 47.71 kJ/mol and 40.95 kJ/mol.