We report growth of vertically well-aligned ZnO nanowires on ZnO:Ga/glass templates and the fabrication of resistive ZnO nanowire-based oxygen gas sensor. It was found that the ZnO nanowires are grown preferred oriented in the (002) direction with a small x-ray diffraction full-width-half-maximum. From high resolution transmission electron microscopy, scanning electron microscopy and micro-Raman measurements, it was found that the ZnO nanowires prepared in this study are single crystalline with good crystal quality. It was also found that measured sample resistance increased logarithmically as the oxygen gas pressure in the chamber was increased. Such a relationship suggests that the device is potentially useful for resistive oxygen gas sensing at room temperature.