There is provided an oxidizing gas sensor that includes an insulating substrate, a gas sensing layer laminated on the insulating substrate and substantially made of tin oxide so as to make resistance changes in response to concentration variations in oxidizing gas and a plurality of catalyst grains applied to a surface of the gas sensing layer and substantially made of gold, wherein 20% or more of the catalyst grains have an aspect ratio of 2.0 or greater when viewed at from the surface of the gas sensing layer.