ZnO thin films were deposited on sapphire (α-Al2O3) substrates by RF magnetron sputtering at substrate temperatures of 500, 600, 650 and 700°C for 3h at rf-powers ranging from 60 to 120 W. The FWHM of the XRD (0002) peak for the ZnO film was reduced down to 0.07° by optimizing the chamber pressure at a substrate temperature of 700°C. Sharp near-band-edge emission was observed in the photoluminescence (PL) spectrum for the ZnO film grown at room temperature. Excess RF power aggravates the crystallinity and the surface roughness of the ZnO thin film. Pole figure, AES and PL analysis results confirm us that RF magnetron sputtering offers ZnO films with a lower density of crystallographic defects. ZnO films with a high quality can be obtained by optimizing the substrate temperature, RF power, and pressure of the RF magnetron sputtering process.