Direct decomposition of NO into N-2 and O-2 on a C-type cubic (Gd1-x-y YxBay)(2)O3-y solid solution catalyst is investigated. These novel catalysts are found to exhibit higher activity and conversion rates than conventional La-containing perovskite oxide catalysts for NO decomposition. C-type cubic (Gdl-x-y Y-x-Ba-y)(2)O3-y catalysts are therefore considered to be possible candidates for the conversion of harmful exhaust gases.