A gas sensor suppresses the deterioration of gas tightness caused by failure of a sealing material. The gas sensor includes: a housing; a sensor element arranged inside the housing; a sealing material filling a gap between the sensor element and the housing; an insulation member arranged on a proximal end side of the sealing material; and an annular metal ring arranged on a proximal end side of the insulation member. The sealing material, the insulation member and the metal ring are fixed under pressure by caulking from a proximal end side to a distal. A proximal-end facing surface of an inner peripheral portion of the metal ring is spaced apart from the caulking portion in an opposing region where an inner end of the caulking portion and the metal ring face each other in an opposed manner.