Carbon nanotube (CNT) gas sensors for NOx gas detection were prepared. CNTs were grown on an Al2O3 substrate with interdigital Pt-electrodes (Al2O3 ceramic substrate) using both pulsed laser deposition (PLD) and thermal chemical vapor deposition (CVD) method. In this method, Al buffer layer and Fe catalytic thin film were prepared on the substrate by PLD method and then CNTs were grown by thermal CVD method. Surface images of CNTs on the substrates were observed by SEM, and the gas sensing property specific to NO gas was measured. Resistance of the prepared CNTs gas sensor decreased with increase of sensor temperature, and it decreased with increase of NO gas concentration at room temperature.