In order to improve NOx gas sensors' sensitivity, we have prepared TiO2 doped ZnFe2O4 (ZFTO) epitaxial thin films with different thicknesses on Yttria stabilized-ZrO2,YSZ(100) substrate by pulsed laser deposition. Pt interdigital electrodes were deposited on the films by DC sputtering. The resistance of the films was measured during NO2 gas adsorption-desorption cycles. As a result, ZFTO films exhibited the highest sens tivity (燃/Rair) when the operating temperature was approximately 200oC and thickness of 50nm.