The grain size distributions (diameter and aspect ratio) of porous Si3N4 ceramics composed of elongated beta -Si3N4 grains were evaluated statistically, and their effect on the pore size distribution and the flexural strength of the porous Si3N4 was investigated. Porous Si3N4 ceramics having porosities of 27 to 43% and median pore diameters of 0.56 to 0.96 mum were used as specimens. The grain diameter distribution was well correlated to the pore size distribution of the porous Si3N4 ceramics. We concluded that the strength of the porous Si3N4 ceramics increased with increasing grain length of beta -Si3N4 as well as with decreasing porosity.