PROBLEM TO BE SOLVED: To provide a gas sensor element configured to prevent reduction in response performance even if ethanol is contained in a fuel or an exhaust gas or the content thereof is large.SOLUTION: A gas sensor element 10 includes: a solid electrolyte layer 3 having a pair of electrodes 4 comprising a measured gas-side electrode 41 and a reference gas-side electrode 42 arranged on both sides; a porous diffusion resistance layer 2 surrounding the measured gas-side electrode 41 via a measured gas space 8a; a shield layer 1 which forms the measured gas space with the porous diffusion resistance layer 2; a reference gas space protective layer 5 surrounding the reference gas-side electrode 42 via a reference gas space 8b; and a catalyst-carrying protective layer 9 formed on an outside surface of the porous diffusion resistance layer 2 at least. The catalyst-carrying protective layer 9 contains a non-noble metal catalyst 92 and an oxide 93 of alkali metal or an oxide of alkali earth metal.
