Abstract: The constant stress creep behavior at 350 ℃ was investigated for Al₂O₃ fiber reinforced Al based composite fabricated by squeeze casting. During the interrupted creep process, the variations of microstructure were observed by means of SEM. The fracture of fibers, the debonding of fiber and matrix, and the deformation of matrix were found in creep of composite materials. On the basis of the changes of microstructure in three phases of creep, the creep behavior of the composite was analyzed. It is suggested that the glide and climb of dislocation around fibers contribute to creep of the composite.The authors propound a rupture mechanism of short fiber reinforced MMCs, which succeeds in interpreting the three stages of creep for composites.