Epoxy network systems were prepared based on diglycidyl ether of bisphenol A with two kinds of low molecular weight polysiloxane, aminopropyldimethyl-terminated polysiloxane and phenyl-terminated polysiloxane. Their physical ageing phenomena were studied by differential scanning calorimetry. The calorimetric data obtained after annealing the neat and the modified cured epoxy resins at 175 degrees C show that two kinds of relaxation-internal stress relaxation and enthalpy relaxation-take place simultaneously during annealing. Furthermore, the extent and the rate of relaxation are closely related to the kind of modifiers and their ratio.