Aluminum oxynitride (AlON) powders were prepared by solid-state reaction processing with α-Al₂O₃ and AlN as starting materials in nitrogen atmosphere. The effects of reactive temperature, holding time, and Al₂O₃/AlN ratio on the resultant phase compositions were investigated systematically by XRD. In addition, the reactive mechanism was tentatively explored. The experimental results indicate that the solid-state reaction for AlON is mostly controlled by thermodynamics and the dynamic factors are also important to the reaction. The reaction can not be thoroughly processed neither only by prolonging holding time at lower reactive temperature nor only by increasing reactive temperature in a shorter holding time. Both reactive temperature and holding time are crucial to the reactive progress. By diffusing AlN into Al2O3 lattice, O-riched AlON formations begin between 1600℃ and 1650℃, and finish at about 1750℃. Above 1800℃, O-riched AlON converts into Nriched AlON by further diffusing remnant AlN into Al2O3 lattice. Pure AlON is prepared by the solidstate reaction of Al2O3 and AlN at 1950℃ in nitrogen atmosphere for 4h.