Niobium-doped Mg x Zn 1−x O (Nb-MZO) mixed oxide films with high transmittance were successfully deposited on sapphire substrates through radio-frequency (RF) magnetron sputtering using a 4-in ZnO/MgO/NbO x (75/20/5 wt%) target. In this study, the films were analyzed using Hall measurements, X-ray diffraction (XRD), transparent performance measurements, and X-ray photoelectron spectroscopy (XPS). XRD results showed two peaks: MgO 2 ( 002)-wurtzite and Mg x Zn 1−x O (111)-cubic peaks. The Nb-MZO films exhibited high transparency, with transmittance exceeding 90% in the visible region and a sharp absorption edge in the ultraviolet (UV) region, implying that the MgO content in the Nb-MZO layer increased the bandgaps. These results indicate that Nb-MZO films are ideal for use as transparent contact layers in near-UV light-emitting diodes. Hall measurements and XPS results successfully demonstrated the p-type conductivity of the Nb-MZO films because of the composition of the N-Nb binding caused by annealing in nitrogen atmosphere.