The high-performance and low-cost ultraviolet photodetectors are promising for wide applications in many important fields. In this paper, well-aligned zinc oxide nanowire arrays (ZNWAs) were first grown on an indium tin oxide (ITO) coated glass substrate by a facile chemical bath deposition method at low temperature. The ZnO nanowires were 30-60 nm in diameter and 600-900 nm in length. Then poly (9-vinayl carbazole) (PVK) thin films were deposited on the ZNWAs, and a ZNWAs/PVK heterojunction ultraviolet photodetector was built. The results show that the ultraviolet photodetector displays good response to 365 nm light. By calculation, its sensitivity, responsivity, detectivity, response time, and decay time at a wavelength of 365 nm were 15.33 (voltage of 0.05 V), 37.72 A/W (voltage of 2 V), 1.29×10¹² Jones, 12.6 s, and 34.2 s, respectively.