Epitaxial ZnO films are grown on Al2O3 (0001) by the MOCVD method. These films are high quality wurtzite crystals with (0001) orientation. Big hexagonal crystallites (diameter from several decades to 100 μm) are found on the surface. Inside these crystallites, a stronger luminescence is observed compared with the plain area.Transmission electronic microscopy reveals that the film is thicker inside the hexagonal crystallites than the plain area, and some crystallites are not connected with each other and are slightly rotated with respect to their neighbours.