Rod-like single-phase crystals of Y-alpha-SiAlON were synthesized by combustion of Si, Al, alpha-Si3N4, SiO2 and Y2O3 powders. The effects of nitrogen pressure and NH4F additive on combustion synthesis (CS) of rod-like alpha-SiAlON crystals were investigated. In absence of additives, non-reacted silicon powder was found in the combustion products, while the products comprised only alpha-SiAlON. Small additions (up to -5 wt.-%) of NH4F favours the disappearance of non-reacted silicon from the CS products, but further amounts promotes the formation of beta-SiAlON, which tends to become the predominant phase in the reaction products. Experimental results showed that alpha-SiAlON was easily formed at low nitrogen pressure values.