Porous silicon nitride (Si 3 N 4) ceramics with highly ordered and unidirectionally aligned channels were fabricated by extrusion method using nylon fibers as the pore forming agent. The microstructure, mechanical properties and gas permeability were investigated. The results showed that the added nylon fibers were mostly converted to pores, the average pore diameter was approximately 19.5 µm and shrank about 22% from the size of original pore former (25 µm) during sintering. The porosity and gas permeability increased and the 3-point bending strength decreased proportionally with increasing the nylon fiber content. When the nylon fiber content increased to 20 wt.%, the porosity, bending strength and gas permeability of the extruded samples with uni-directionally aligned pores were higher than those of non-extruded sample with random pores. For the extruded samples, the resulting porous silicon nitride ceramics showed a high gas permeability owing to their unidirectionally oriented structure.