By means of scanning electron microscopope and X-ray diffraction, microstructural evolution of well-aligned ZnO nanorod array films was studied. The films were prepared on a glass using direct deposition method in an aqueous solution. The experimental results show that the highly oriented rods grew from the randomly oriented crystals. Those rod-like randomly oriented crystals began to impinge on other neighboring crystals and their growth became physically limited; only the rods perpendicular to the substrate were allowed to grow freely. This kinetically controlled nucleation and growth would be responsible for producing the uniformly oriented nanorods. During the ZnO rods’ growth, the topology of their top faces changed from fiat, prismatic to finally flat.