Highly porous Si3N4 ceramics with bimodal pore structure were prepared by the extrusion processing with petroleum coke of 30 m as pore-maker. The microstructure, mechanical strength, and gas permeability were investigated. The microstructure with petroleum coke contained not only numerous fine pores by interlocking the high aspect ratio -Si3N4 grains, but also some large pores of 15-25 m left by the burnout of petroleum coke. The resultant samples obtained an improved gas permeability of 1.2 x 10(-12) m(2), which is approximately two times that of samples without petroleum coke addition. Furthermore, the mechanical strength is still superior even at a porosity of 67% in comparison with the other porous ceramics used in the current diesel particulate filter.