Highly efficient photocatalytic ZnO nanoneedle arrays with a large surface/volume ratio were prepared on inexpensive, large-area substrates using metal-organic chemical vapor deposition. The photocatalytic activity of ZnO nanoneedle arrays is much enhanced due to their increased surface/volume ratio. It is believed that the "bottom-up" approach may be expanded to create many other one-dimensional oxide semiconductor nanostructures (see Figure).