Aluminum oxynitride spinel (AlON) powders were synthesized by aluminothermic reaction in a reducing N2-CO atmosphere. Low cost and easily available aluminum and γ-Al2O3 alumina micrometer-sized powders were employed as starting materials. Mixed powders consisting of 75 wt% Al and 25 wt% Al2O3 were milled together and pressed into billets with diameter of 20 mm and height of 15 mm. Green-body billets were then calcined in charcoal-protected condition (namely in a N2-CO atmosphere) at 1600°C. Phase composition and microstructure of final sintered products were analyzed. The results showed that AlON phase with AlN as a minor phase was formed at 1600°C for 3 h. At the same time, grains of AlON were tabular in shape and whiskers can be found in samples after being sintered at 1600°C.