A gas sensor element is disclosed having a solid electrolyte body having oxygen ion conductivity, a measuring gas detecting electrode and a reference gas detecting electrode formed on both surfaces of the solid electrolyte body, respectively, a diffusion resistance layer formed on the one surface of the solid electrolyte body so as to surround the measuring gas detecting electrode and available to permeate measuring gas to the measuring gas detecting electrode, and a catalyst-supported trap layer formed on an outer side surface of the diffusion resistance layer. The catalyst-supported trap layer has an average film thickness of a value ranging from 20 to 200μm, and an amount of the supported catalyst with respect to a gross weight of the catalyst-supported trap layer lies in a value ranging from 0.1 to 2 wt %.