Abstract: The effects of stress, temperature and heat-treatment on the steady state creep rate of 22vol% short Mullite fiber reinforced LY12 composites were studied. A creep mehanism of cxunposites was advanced. The creep behavior of composites was controlled by the climb of dislocation at low stress state and by the interface conditions at high stress state. The interfac, of cxunposites was analysed by TEM.