In this paper, the preparation of reaction sialon suspensions containing Si3N4, A1N, Y2O3 and A1(2)O(3) has been investigated as a way to achieve an optimum degree of homogeneity in the green body microstructure. The four starting powders have different specific gravity, particle size and surface chemistry, therefore sedimentation tests, together with determination of rheogical properties were performed using suspensions of the four starting powders separately. The results show that they have similar dispersing ability in a solvent containing 60-vol% Methyl-ethyl-ketone and 40-vol% ethanol using hypermer KD1 as dispersant. A 50-vol% reaction sialon suspension has been prepared using 3-wt% KD1, the suspension shows near Newtonian flow behaviour and is stable after ageing for up to 3 days. The slip casting green body from this suspension has a uniform microstructure as observed by SEM and quantified by pore size distribution. The uniformity and high density of the green body enhances the sintering behaviour, so that a near full dense alpha-sialon ceramics can be obtained through pressureless sintering at a relative low temperature of 1750degreesC for 2 hours.