In this paper, ZnO nanorods self-assembled nanospheres were synthetized by a hydrothermal route, an ultraviolet (UV) photodetector was constructed based on the ZnO nanospheres, the crystal structure, morphology and device performance of the nanospheres were systematically examined. The results revealed that a large number of single-crystalline ZnO nanorods were self-assembled into nanospheres, the nanorods were 80-120 nm in diameter. The ZnO nanospheres UV photodetector was found to have excellent performance, the values of photocurrent gain, responsivity, detectivity, external quantum efficiency, rise time and decay time for the photodetector were 318.5 at 5 V, 93.7 A/W at 5 V, 2.7 ? 1012 Jones, 3.2 ′ 104%, 4.3 s and 7.4 s, respectively. Such high performance was mainly attributed to forming a great number of UV light absorption antennas by ZnO nanorods in the device.