The present paper deals with the pressure infiltration of short fiber preforms by molten magnesium alloys. Saffil aluminum oxide fibers and AZ91 and AS41 matrix alloys were the materials selected for the composites. The mechanical and physical properties of the composites were measured. Significant changes from the matrix alloy properties were noted, indicating that considerable improvements in the performance of cast, commercial magnesium alloys can be achieved by short fiber reinforcement of this type. The experience gained in the study demonstrates that exploitation of the technology depends upon the availability of high quality preforms and control of the thermal conditions during casting.