A ceramic membrane filter was developed by depositing ultrafine powders onto a porous substrate. The powders, having an average particle size of tens of nanometers, were produced by a newly developed technology, pulsed wire discharge: The carrier gas was pumped through the porous substrate, which had been heated to 500 degrees -700 degreesC, so that the powders could be sintered on the substrate surface, resulting in a membrane filter. Gas separation experiments were conducted using this filter. The experimental results showed a ratio of gas permeation very close to that given by the Knudsen flow.