A gas sensor (1) including: a sensor element (10) which includes a detection portion (11) and a heater (50); a metal shell (138); and a filled member (153) filled with a filling material between the metal shell and the sensor element, wherein a position at which change in a temperature of the sensor element is smallest when a disturbance is applied is a temperature reference position M, the filled member is positioned rearward of the temperature reference position, an overall axial length LT of the sensor element is not greater than 50 mm, an axial length LE from a rear end of the filled member to a rear end of the sensor element is not smaller than 13.5 mm, and an axial length LA from the temperature reference position to a front end of the filled member is greater than 5.0 mm and not greater than 11.5 mm.