A gas sensor is provided which has improved responsiveness and is capable of improving accuracy in measurement of an imbalance between cylinders. The gas sensor includes a solid electrolyte having oxygen ion conductivity, a measurement electrode mounted on one principal surface of the solid electrolyte and is exposed to measurement gas, and a reference electrode mounted on the other principal surface of the solid electrolyte and exposed to reference gas A. Interface capacitance between crystal particles constituting the solid electrolyte is not more than 150 μF. Interface resistance between the crystal particles constituting the solid electrolyte and each of the measurement electrode and the reference electrode is not more than 80 Ω. The measurement electrode has a film thickness t1 of 2 to 8 μm.