A process for manufacturing a porous Si.sub.3 N.sub.4 ceramic filter, wherein silicon powder, the raw material, methyl cellulose, the binding agent, and water, the solvent, are well-mixed together to obtain a slurry. A sponge is then dipped into the slurry to adsorb the slurry. After drying the sponge in an oven, it is biscuit fired at 350.degree. C. for 2 hours, and then sintered at 1200-1400.degree. C. for 15 hours.