A gas sensor (200) includes a gas sensor element (10) extending in the direction of an axis O, and a housing (50) made of metal, radially surrounding the gas sensor element, and adapted for inserting at least partially into a sensor-mounting hole (350) of a mounting body (300). The gas sensor (200) further includes a resin member (60, 61) which radially surrounds the housing at least partially and having a contact portion (C) in contact with the housing that is at least partially disposed axially frontward with respect to the outer surface of the mounting body (300) around the sensor-mounting hole, and a heat sink member (80) that is in contact with the housing at an axial position the same as or located frontward of the axial position of the front end of the contact portion.