Fly ashes from various sources were used to synthesise alpha-and beta -sialon's by carbothermal reduction and nitridation. Both beta -sialon as well as alpha/beta -sialon composites can be obtained depending on the overall composition of the fly ash. The alpha/beta ratio is not only influenced by the overall composition of the fly ash but also by the time and temperature of the carbothermal conversion. The sialon powders obtained by carbothermal synthesis were used for preparation of compacts using either pressing or slip casting. After sintering, both methods yield similar final densities and mechanical properties, Sialon ceramics with mechanical properties similar to sialon's made of clay can be obtained from fly ashes.