An epitaxial ZnO thin film was entirely fabricated by pulsed laser deposition.Both the orientation and the size of the crystallites were studied.The X-ray diffraction (XRD) patterns of the film show strong c-axis oriented crystal structure with preferred (002) orientation.The Phi-scan XRD pattern confirms that the epitaxial ZnO exhibits a singledomain wurtzite structure with hexagonal symmetry.In situ high-temperature XRD studies of ZnO thin film show that the crystallite size increases with increasing temperature,and (002) peaks shift systematically toward lower 2θ values due to the change of lattice parameters.The lattice parameters show linear increase in their values with increasing temperature. An epitaxial ZnO thin film was entirely fabricated by pulsed laser deposition. Both the orientation and the size of the crystallites were studied. X-ray diffraction (XRD) patterns of the film show strong c-axis oriented crystal structure with a preferred (002) orientation. Phi-scan XRD pattern confirms that the epitaxial ZnO exhibits a singledomain wurtzite structure with hexagonal symmetry. In situ high-temperature XRD studies of ZnO thin film show that the crystallite size increases with increasing temperature, and (002) peaks shift systematically toward lower 2θ values ​​due to the change of lattice parameters. The lattice parameters show linear increase in their values ​​with increasing temperature.