The mechanical properties of Al/Al₂O₃composites have been investigated in relation with manufacturing factors such as applied pressure of casting and binder amount of preform. It was found that tensile strength increases with an increase of applied pressure, but decreases with binder amount. Increase of tensile strength is attributable to refinement of microstructure, improvement of intefacial bonding between Al₂O₃short fiber and matrix, decrease of porosity in the matrix. Due to the high thermal stability of alumina short fiber, tensile strength of composites at 150℃ was superior to matrix alloy at room temperature. To evaluate the strength of composites, modified Kelly-Tyson`s equation was introduced. Manufacturing factor M was obtained calculating from experimental data. M values were increased with applied pressure, but decreased with binder amount. The initiation of microcrack appeared to be at interface and reinforcement colony. Amount of micro-dimple was increased with applied pressure, and interfacial debonding phenomenon was remarkable with an increase of binder amount.