With the assistance of mechanical activation, yttrium-stabilized alpha-SiAlON was prepared by combustion synthesis in air, instead of high-pressure N-2 atmosphere for the first time. The reaction activity of metallic particles was remarkably enhanced by mechanical activation, which conduced the reduction of grain size, increased the total surface area and formation of fresh surface. The formation of a-SiAlON by combustion synthesis in air was explained by a kinetically induced reaction mechanism, in which both initial formation of alpha-SiAlON and following avoidance of oxidation were fulfilled by the retardation of 02 infiltration owing to the short reaction period and fast cooling rate. (C) 2006 Elsevier Ltd. All rights reserved.