The synthesis method of aluminium oxynitride (AlON) powders by nitriding of Al/Al2O3 mixture under highpressure nitrogen is proposed. The novelty of this method consists in adding KClO4 or Mg(ClO4)2 and extra Al into the starting mixture (Al+Al2O3) to cause the exothermal aluminium oxidation reaction, which therefore initiates the aluminium nitriding reaction. The microstructure and phase composition of the AlON powders obtained by self-propagating high-temperature synthesis are demonstrated by means of SEM and XRD analysis. Diffuse reflection spectra of AlON powders have been measured and the values of band-gap energy have been calculated. Optical transmission and reflection characteristics of the AlON ceramic samples sintered from AlON powders at 1930°C have been studied. The influence of the technological parameters of ceramics production on their transparency is revealed – the most transparent sample is obtained from the powders synthesized with the Mg(ClO4)2 additive and sintered for 6 h.