The effect of MgO buffer layer on the structural properties of sputter-grown ZnO thin film was investigated. Sapphire (0001) and Si (100) substrate were used for the growth and MgO buffer layer was inserted between ZnO thin film and the substrate. X-ray diffraction pattern indicated that enhanced crystallinity in the ZnO thin film grown was achieved by inserting very thin MgO buffer layer, regardless of the substrate type. The strain in the ZnO thin film could also be controlled by the insertion of the MgO buffer layer, and tendency of the strain was strongly dependent on the substrate type.