Defect-related photoconductiyity of single ZnO nanowires is investigated. The photoconductivity shows powerlaw dependence with incident green laser intensity due to the defect mechanisms including both recombination centres and traps. The device based on single ZnO nanowire shows a sensitive photoresponse to green light with significant on/off ratios. In addition, the photocurrent is highly sensitive to the polarization of the incident illumination. Therefore, the nanowire may act as a polarized photodetector.