All oxide-based, nano-transparent p-n heterojunction device consisting of p-NiO and n-ZnO thin films was fabricated by r.f. sputtering method. The structural and electric properties of the p-NiO/n-ZnO heterojunction were characterized by X-ray diffraction (XRD), UV-visible spectroscopy, Hall measurement, and photocurrent measurements. The XRD shows that ZnO films are highly crystalline in nature with a preferred orientation along the (0 0 2) direction. The p-NiO/n-ZnO heterojunction device has an average transmittance of over 80% in the visible region. The current-voltage curve of the heterojunction demonstrates obvious rectifying diode behavior in a dark environment. The lowest leakage current is 4.35×10-8 A/cm2 for p-NiO/n-ZnO heterojunction device. The realization of all-wide-band-gap p-NiO/n-ZnO heterojunction will provide a promising application of UV light emitting diodes.