The physical aging behavior of fully and partially cured epoxy resins based on diglycidyl ether of bisphenol A(DGEBA) has been investigated by differential scanning calorimetry (DSC). A sub-T-g heat flow transition (T-g1) could not be attributed to the phase separation or dynamic mechanical relaxation, as reported in the literature. In both fully and partially cured epoxy resins, it occurs only when the cooling rate is higher than that having the lowest T-g in the DSC scan. Therefore, it could be attributed to the motion of the internal stress-relaxed molecular chain.