The properties of 21 different ceramics of ß'-Si3Al3O3N5 were measured. The sialons were prepared by three methods: reaction sintering in a gas pressure sintering furnace, reaction hot-pressing and sintering of sialon powder produced by carbothermal reaction from kaolin. Furthermore, the series differed in kind (CeO2 or CaO) and concentration of additive and process conditions. The quantities measured were composition (X-ray diffraction), density, microstructure, Vickers hardness (2 N), Young's modulus, Poisson's ratio, fracture toughness (SEN B) and biaxial strength. Generally the room temperature properties were hardly influenced by the production route, composition or process conditions. Fracture toughness and bi-axial strength were most sensitive to the process conditions. The mechanical properties of kaolin-derived sialon appeared to be as good as those of the other sialons.