In the present study we have fabricated NiO:Cu/ZnO pn heterojunctions at various substrate temperatures by magnetron sputtering method.X-ray diffraction (XRD) a nalyses reveal the formation of wurtzite-type ZnO structure,and NiO:Cu films show polycrystalline when the substrate temperatu re is set at room temperature. The (111) peaks of NiO:Cu are improved obviously with increasing substrate tempe rature.However,(002) peaks of ZnO are depressed at higher substrate temperature of 400℃.Furthermore, the right-shift of (111) peaks of NiO:Cu with the substrate temperature indicates that the c axis distances shrink .It can be explained by that the strain caused by lattice mismatch between NiO:Cu films and substrates will be relaxed a nd the native defects will be decreased in the heterojunctions through increasing substrate temperature.The i mprovement of crystalline in heterojunctions contributes to the increased optical transmittances and the decreased optical gaps of NiO:Cu films when the substrate temperature increases.Typical rectifying proper ties are shown in the heterojunctions and the best rectifying property appears at 300℃,which can be attributed to the decreased defects, which is also evidenced by the results of XRD,atom force microscope (AFM) and UV spectra.Good rectification behavior and high optical transmittance in NiO:Cu/ZnO pn heterojunctions indicate that they have the application prospect of future transparent optoelectronic devices.