A new method for fabricating porous silicon nitride ceramics has been developed by using fly ash cenosphere (FAC) with mean diameter of 87μm as a pore-forming agent. Sintering was carried out at 1780°C for 2h under a nitrogen atmosphere. FAC can also act as a sintering aid besides a pore-forming agent. X-ray diffraction (XRD) and transmission electron microscopy (TEM) studies showed that YSiO 2 N forms instead of Y 2 Si 3 O 3 N 4 when FAC is incorporated. Microstructural analysis revealed that large spherical cavities are scattered in a relative dense matrix. Porous Si 3 N 4 ceramics with density of 2.17–2.30g/cm 3 , Young’s modulus of 141–150GPa and strength of 180–320MPa were obtained by changing the FAC content.