A gas sensor includes a gas sensor element that extends in an axial direction and that includes a detector, which detects a specific gas in a mixed gas; a metal shell that surrounds a periphery of the gas sensor element to hold the gas sensor element; a base that is disposed on a rear side of the metal shell and that covers a rear end portion of the gas sensor element, the base being made of a polymer material; and a metal tube that connects the metal shell and the base to each other and that includes a rear portion and a front portion, the rear portion being integrated with the base, the front portion forming an exposed portion that is exposed from the base. A part of the exposed portion of the tube is connected to the metal shell, and the base is disposed apart from the metal shell.