A gas sensor is provided with a sensor element having a detecting portion; an insulator supporting the sensor element in a state where the detecting portion is protruded therefrom, the sensor element being inserted through the insulator; a housing supporting the insulator; an inner cover covering the detecting portion; and an outer cover covering the inner cover.An inner flange portion of the inner cover and an outer flange portion of the outer cover are supported between the insulator and the housing. A protrusion is formed on a corner portion facing the insulator, the protrusion contacting with the insulator. An end face of the outer flange portion is positioned radially closer to an outer side with respect to a radial direction, than a position of an end face of the inner flange portion.