Vertically aligned ZnO nanowire arrays were grown on ZnO single crystals using a chemical vapor deposition method. Nucleation sites were defined by patterning Au nanodot catalysts fabricated through anodized aluminum oxide (AAO) templates. Morphology and structure characterizations showed that the as-grown nanowires had the single-crystal hexagonal wurtzite structure with a <0001> growth direction. By changing the pore distance of AAO, the density of nanowires could be well controlled. A sharp peak in the UV region and a weak broad peak in the visible region were shown in the room temperature photoluminescence spectra, suggesting the high-quality ZnO nanowire arrays were obtained.