The strength and structure of -sialon ceramics prepared by slip casting with a different degree of flocculation was investigated. Commercial -sialon (z=0.5) powder with 7 wt.% Y2O3 as sintering additive powder was used. Four different suspensions were prepared ranging from completely deflocculated to strongly flocculated. The degree of flocculation was checked with zeta potential and rheology investigations. The mechanical properties and microstructure of the green material reflected the varying degree of flocculation. After sintering, the various sintered materials showed similar mechanical properties for all ceramics. The strength was about 850 MPa, the toughness 4.4 MPa m1/2 and hardness about 15.8 GPa. Accordingly the different green products were homogenised during sintering. This occurred even for samples with very low green density thanks to the favourable powder characteristics (shape, distribution, chemical composition) and liquid phase sintering with sufficient amount of sintering additive.