Porous -Si3N4 ceramics are sintered at 1600 degrees C in N-2 and postheat treated at 1500 degrees C under vacuum using Li2O and Y2O3 as the sintering additives. The partial sintering and phase transformation are promoted at low temperature by the addition of Li2O. The addition of Y2O3 is advantageous for the formation of high aspect ratio -Si3N4 grains. After postheat treatment, a large amount of intergranular glassy phase is removed, and the Li content in the samples is decreased. By this method, the -Si3N4 porous ceramic with a porosity of 54.1% and high flexural strength of 110 +/- 8.1MPa can be prepared with a small amount of sintering additives, 0.66wt% Li2O and 0.33wt% Y2O3, and it is suitable for high-temperature applications.