Silicon nitride porous body and its production process

A process for producing a silicon nitride porous body which is a body having a generally columnar outer shape and at least two through-holes mutually parallel to one another and which has generally perpendicularly oriented columnar crystals on the surface of the through-holes, which process comprises adding a molding aid and water to a mixture which comprises 100 parts by mass of metal silicon particles having an average particle diameter of from 1 to 150 μm and from 0.2 to 45 parts by mass, as calculated as SiO2, of silicon oxide particles and wherein the total amount of the metal silicon particles and the silicon oxide particles is at least 80 mass % in the mixture, followed by kneading to obtain a kneaded product, then extrusion molding the kneaded product by means of a mold to obtain an extrusion molded product having a cross-sectional area per through-hole of from 1 to 100 mm2, and then heat-treating the extrusion molded product in nitrogen to nitride the metal silicon.