α-β SiAlON ceramics were produced from different starting Si3N4 powders including P-Si3N4 and α-Si3N4 powders and mixtures of these powders. Gas pressure sintering was used for sintering. After sintering, resultant fracture toughness values were correlated with microstructure and starting powders. By optimizing chemistry and process parameters; α-β SiAlON ceramics with reasonable fracture toughness can be produced from rather coarse β-Si 3N4 powder. This could improve the economic viability of SiAlON ceramics since β-Si3N4 powders are less costly.