Self-reinforcement of Li-alpha -sialon ceramics by in situ growth of elongated alpha and beta -sialon grains has been explored and analysed. Properties of Li-alpha -sialon ceramics are mainly determined by the overall starting composition and the crystalline modification of the starting Si3N4 powder which in turn determine the final microstructure of the materials. Both the morphology and crystalline phase of the elongated sialon grains have strong effects on the toughening mechanism. The results indicate that alpha -sialons reinforced by elongated beta -sialon grains have advantages over similar materials reinforced by elongated alpha -sialon grains because of the type of crack deflection toughening mechanism involved.