Ultrafine Ru particles were dispersed in micropores of activated carbon fiber (ACF). NO was efficiently and rapidly reduced to N-2 on the Ru particles through the disproportionation reaction of 3(NO)(2) = 2 NO2 + 2 N2O in the micropore spaces at 303 K. The N-2 yield at 303 K was 0.8, and the half-life of the reduction reaction was 3 min. The amounts of the byproducts N2O and NO2 on Ru-tailored ACF at 303 K were less than 0.25%. The oxygen was not evolved at 303 K.