All inorganic, self-powered, narrowband, and rapid response p-NiO/n-ZnO nanowire (NW) ultraviolet (UV) photodetectors were fabricated and investigated with Al2O3 as an interface modification layer. Al2O3 films grown by atomic layer deposition can greatly suppress the surface defects on ZnO NWs and improve the p-NiO/n-ZnO NW interface. The photo-response of the photodetector in the 430–500 nm wavelength range was greatly inhibited and the full-width at half-maximum of the response spectrum was less than 30 nm. A large responsivity of 1.4 mA/W was achieved under a 380 nm UV irradiation (0.36 mW/cm2) at zero bias and the response time of the device was less than 0.04 s. Such a simple interface modification method might promote the developing of ZnO NW based narrowband photodetectors.