The crystal structure conversion of Al2O3 during high-energy ball milling was investigated in this paper. γ-Al2O3, which with high reaction activation transformed to α-Al2O3 along with ball milling. After 20 hours milling, a part of Al2O3 became amorphous and AlN was observed in powder. The crystal structure of AlN gained during ball milling was cubic, differed from regular hexagonal AlN synthesized by carbothermal reduction.