PURPOSE: To obtain an alumina-boria whisker reinforced Al-based composite material having high strength.

CONSTITUTION: When an alumina-boria whisker reinforced Al-based composite material is composed of alumina-boria whiskers as a reinforcing material and an Mg-contg. Al alloy as a matrix, 0.03, 0.8wt.% B is incorporated into the Al allay. Since this B reacts with Mg in the matrix, the reaction of B2O3 in the whiskers with Mg in the matrix is inhibited and the formation of a spinel layer and the lowering of the strength of the whiskers due to the formation are avoided.