Al2O3 and AlN powder mixtures were used to synthesise AlON ceramics using the reactive spark plasma sintering (SPS) method at temperatures between 1400 and 1650 degrees C for 15-45 min at 40 MPa under N-2 gas flow. AlON phase formation was initiated in the samples sintered above 1430 degrees C, according to the X-ray analysis. The complete transformation of the initial phases (Al2O3 and AlN) into AlON was observed in the samples that were spark plasma sintered at 1650 degrees C for 30 min at 40 MPa. A high spark plasma sintering temperature together with a low heating rate produced a greater amount of AlON formation at a constant process time. The densification, microstructure and mechanical properties of the produced ceramics were analysed. The highest hardness value was recorded to be 16.7 GPa, and the fracture toughness of the sample with the highest AlON ratio was measured to be 3.95 MPa m(1/2). (C) 2011 Elsevier Ltd. All rights reserved.