ZnO thin films were epitaxially grown on A12O3 (0001) single crystalline substrate by RF magnetron sputtering. The films were grown at the substrate temperature of 550°C and 600°C for 1 h and at a power of 60–120 W. The crystalline structure of the ZnO films was analyzed by 4-circle X-ray diffraction and backscattering (BS)/channeling. The FWHM of XRD ø -rocking curve increase from 9.45 to 18 arc-min. as the RF power increased from 80 to 120 W at 550°C. In-plane ZnO growth on sapphire.(0001) substrate at 550°C and at 80 W was found to be ZnO  |: A12O3, indicating a 30° rotation of ZnO unit cell about the sapphire (0001) substrate. For a specimen that was grown at an RF power of 120 W, 550°C, 1 h, the FWHM of XRD ø -rocking curve was 7.79 arc-min. In BS/channeling studies, the films deposited at 120 W, 600°C showed good crystallinity with the channeling yield minimum (Xmin) of only 5%, but for films deposited at 550°C the yield was as high as 50-60%, was of lower crystalline qualilty. From the results of the AFM measurement, the grain size gradually increased as the growing temperature and power increased. In case of the film deposited at 120 W and 600°C. the hexagonal shape of the grains were clearly observed. In PL measurement, only the sharp near band edge (NBE) emission were observed at room temperature for the film deposited at 80-120 W and 550°C, but the emission from deep level were also detected in the films deposited at 60 W, 550°C and 120 W, 600°C. The FWFM was decreased from 133 meV to 89 meV as RF power increased from 80 to 120 W at 550°C, and that of film deposited at 120 W and 600°C showed 98 meV respectively. The results were somewhat opposite to those of XRD. In the present study, the relationship between optical properties and crystal structure is discussed in terms of the quality of grains and the defects.