A gas sensor is provided with: a sensor element having a solid electrolyte body, a measurement electrode and a reference electrode; a housing into which the sensor element is inserted; and an element cover arranged at the tip-end side of the housing. The element cover has an inner cover arranged so as to cover the tip-end portion of the sensor element from outside, and an outer cover arranged so as to cover the inner cover from outside. When L is defined as an axial distance from a base end of an internal space of the inner cover to the base end of the measurement electrode, an axial distance M from the base end of the internal space of the inner cover to the base end of an inner vent hole positioned in the most base-end side among the inner vent holes provided to the inner cover is 0.2 L to 0.65 L.