In this work, the influence of crystal structure on the friction coefficient of zinc oxide (ZnO) films was studied. The ZnO films were deposited on a Si (100) substrate using an atomic layer deposition process, and the crystal structure of the ZnO films was changed by adjusting the substrate temperature. The surface morphology and the crystal structure of the ZnO films were measured by an atomic force microscope and an X-ray diffractometer, respectively, and the friction coefficient of the ZnO films was measured by a ball-on-disk dry sliding tester. The results show that the ZnO films deposited at substrate temperatures below 200A degrees C are dominated by (100), (002) and (101)-orientated crystals, while the ZnO films deposited at substrate temperatures above 250A degrees C are dominated by (002)-orientated crystals, and that the crystal structure influences the friction coefficient of ZnO films greatly. The ZnO films with (002)-orientated crystals possess a larger friction coefficient than those with other orientated crystals. In order to verify this conclusion, we measured the friction behavior of the ZnO single crystals with different orientations. The results are consistent well with our conclusion.