In this study, a nitriding technique using a mixture of magnesium and alumina powders was applied to aluminum samples. The structure of the resultant film was investigated. The obtained nitride film was composed of two layers. The film hardness gradually changed with increasing depth, and the hardness of the outermost layer was higher than that of the substrate side layer. The outermost layer and substrate side layer were composed of Al₂O₃, Mg, and AlN, and AlN and Al, respectively. Fine MgAl₂O₄ and MgO particles were formed at the interface between the AlN film and the Al substrate.