Abstract: Iron-base GH132 and nickel-base GH33A were selected as two typical superalloys to study creep and stress rupture under complex stress condition at 650℃ and 750℃ respectively. Cyclic stress rupture tests indicate weakening of two superalloys. Cyclic stresses superimposed at creep tests decrease creep fracture lives of both superalloys, but secondary creep rates are generally still controlled by means of stresses at dynamic creep tests, when the amplitudes of superimposed cyclic stresses are not very high.