Zinc oxide (ZnO) p-i-n structured ultraviolet (UV) photodetector has been constructed in this paper. The photodetector exhibits an obvious response to ultraviolet light at 0 V bias, which is a typical character of p-i-n structured photodetectors. The maximum responsivity of the photodetector, which is located at around 390 nm, is about 0.45 mA W at 0 V bias, and the responsivity increases with increasing reverse bias voltage applied. The response decay time of the p-i-n structured photodetector is about 260 ns. This is the first report on ZnO p-i-n homojunction structured photodetectors to the best of our knowledge. Considering that p-i-n structure is the most promising configuration for high performance photodetectors, the results reported in this paper may provide a clue for high-performance ZnO based UV photodetectors.