In order to develop the alumina fiber reinforcements optimized to FRMMCs, the effect of characteristics of alumina fibers on the fabrication process and the characteristics of the alumina fiber reinforced Al alloy composites was investigated. Alumina fibers which have different alumina content were prepared. Alumina content in the fibers was varied from 80% to 100%. Al-4mass%Cu alloy, Al-12mass%Si alloy and Al-10masss%Mg alloy were used as matrix. The FRMMC specimens were fabricated by a low-pressure infiltration process (LPI process). The formability of the preform was improved with increasing alumina content in the fibers. However, broken fibers were observed in the preform when alumina fibers with high alumina content were used. The number of the broken fibers seemed to be increased with increasing alumina content in the fibers. This result could be attributable to a change of fiber strength resulting from a change of alumina content in the fiber. The FRMMC specimens were characterized by using Vickers hardness test. The Vickers hardness of FRMMC specimens depended on the elasticity or the hardness of the fibers. The results obtained suggest that the characteristics of the FRMMCs largely depend on the intrinsic characteristics of the reinforcement fibers.