Aluminum alloy matrix composites reinforced with various amounts of Al₂O₃ short fibers have been produced by rheo-compocasting accompanied by hot pressing. When composites reinforced with fibers are produced by rheo-compocasting, S-L process is the most effective method for homogeneous dispersion of fibers. A sound composites with the improved orientation(3 dimension→2 dimension) of the fibers and increased volume fraction of them have been fabricated through the hot pressing of the casted composites. Fibers are broken down when rheo-compocasting, hot pressing, and T_6 treating. Among them fibers are broken down most heavily in the hot pressing. And even in the case of the composite reinforced with 30vol% fibers, which showed the hardest fiber break down, aspect ratio(11.6) is higher than critical aspect ratio(10.7). The fiber strengthening effect in the composites has showed up to 573K. As the test temperature increases to the range of 573K, the effect has been higher. The fracture of composites is controlled by fiber from room temperature to 473K, but the fracture of composites is controlled by interface between fiber and matrix alloy above 473K.