Porous silicon nitride (Si3N4) ceramics were fabricated by low temperature pressureless sintering, using carbonized rice husk andα-Si3N4 powders as raw materials, and MgO-CeO2 as sintering additives. The effects of CeO2 concentration and sintering temperature on phase composition, microstructure, porosity and flexural strength of the sintered products were investigated by X-ray diffraction (XRD), scanning electronic microscopy (SEM), Archimedes' displacement method and three-point bending strength, re-spectively. The results suggested that MgO-CeO2 was a much more effective sintering additive for Si3N4 than MgO alone. When CeO2 concentration was 4 wt.%–5 wt.% and sintering temperatures were in a range of 1500 to 1550 ℃, the obtained porous silicon nitride ceramics had the porosity of 45.78%–42.81% and flexural strength of 49.44–84.09 MPa. Moreover, when sintering tempera-ture was 1550 ℃ and CeO2 concentration was 5%, large elongatedβ-Si3N4 grains were well developed.