A gas sensor including: a sensor element extending in an axial direction; a metal shell surrounding and supporting the sensor element; an exterior tube that is tubular and is mounted to a rear end of the metal shell; a metal terminal including a first end connected to a lead wire and a second end electrically connected to the sensor element; a separator that is tubular and is disposed in the exterior tube and contains the metal terminal and the sensor element; and a holder being in contact with the separator in the axial direction. The holder includes ribs formed in a frontward face or a rearward face of the holder and arranged at predetermined intervals in a circumferential direction. Each of the ribs occupies a region having a length equal to or greater than a thickness of the holder, as viewed in the axial direction.