A gas sensor element is disclosed which includes a solid electrolyte body, a measurement electrode, a reference electrode, a porous diffusion-resistant layer, a catalyst layer, and a plurality of protective layers. The catalyst layer is provided on an outer surface of the porous diffusion-resistant layer through which a measurement gas is introduced to the measurement electrode. The catalyst layer is comprised of a noble metal catalyst and catalyst-supporting particles. The protective layers are provided in layers on the catalyst layer and comprised of oxide particles. The average particle diameter of the catalyst-supporting particles of the catalyst layer is less than or equal to the average particle diameter of the oxide particles of the one of the protective layers which adjoins the catalyst layer. The further the protective layers are from the catalyst layer, the larger the average particle diameters of the oxide particles of the protective layers are.