Both the growth mechanism and material properties of ZnO epilayers are found to be strongly dependent on slight misorientation of GaN templates. The observation by in situ reflection high-energy electron diffraction and atomic force microscopy reveals that the growth mode changes from a three-dimensional to a two-dimensional growth mechanism, as the misorientation of GaN templates is varied from [0001] just to 0.2 degree toward the a axis. However, ZnO grows under a three-dimensional mode for misorientation toward the m axis. The observed changes in the growth mechanism are discussed in terms of the different surface migration length along the m and a axis, which is caused by the different surface atomic arrangement along the a and m axis. With an increase in the misorientation angle from 0 to 0.2° toward the a axis, the linewidth of (0002) x-ray rocking curve shows a dramatic narrowing from 1768 to 277 arcsec, while the photoluminescence intensity of exciton emission shows a remarkable enhancement by more than one order of magnitude. Such improvement in material properties can be ascribed to the observed change of the growth mode from three- to two-dimensional growth.