Self-propagation high-temperature synthesis (SHS) was applied for the synthesis of low-cost Si 3 N 4 powder. The powder was purified and ground until its particle size reached submicron levels and its purity reached 98%. Using this pretreated powder, with α/β=60/40 content, fully dense Si 3 N 4 ceramics, having improved mechanical properties, were obtained by liquid-phase sintering in the presence of (Y, La) 2 O 3 -AlN. The mechanical properties achieved finally were as follows: strength, 784MPa; hardness, 15.1GPa; and fracture toughness, 5.2MPam 0.5 . The behaviors of the SHS-Si 3 N 4 powders before and after the pretreatment were compared. The relation between microstructure and mechanical properties of the sintered specimens and the effect of different β content in the powder on the sintering process of Si 3 N 4 were also studied.