In this study, we report the fabrication and characterization of a novel nanohetero junction structure (NHJ) UV photodetectors (PDs) on flexible polyethylene terephthalate (PET). The ZnO nanowires (NWs) were grown by 2-step hydrothermal growth (HTG) onto p-type nickel oxide (p-NiO) film deposited PET flexible substrate. For enhancing the quality and reliability of the fabricated UV PDs, the PET substrate was treated with a beforehand thermosetting process to refine its toughness and flatness. By switching the illumination UV light “on” and “off”, the fabricated UV PDs biased under-5 V have an on-off current ratio of 16. After over 100 times 90o bend, the transient measurement almost has the same reversibility but on-off current ratio reducing to 10. These results suggest that the proposed n-ZnO-NWs/p-NiO NHJs on PET flexible PET substrate not only have a fairly good response to UV light but also have good endurance within suitable bend. The present optoelectronic UV sensor would provide an effective and simple way for future developments of flexible optoelectronic devices.