1D ZnO nanostructures have been widely explored due to their potential applications in ultraviolet (UV) region photodetectors because of their unique structural and optoelectronic properties. However, a large number of surface defect states leading to a noticeable dark current hinders their practical applications in UV photodetection. In this work, we have shown improved ZnO/Al2O3 core-shell microrod photodetectors, whose performance is significantly enhanced by defect passivation and the introduction of trap states by atomic layer deposition grown thin amorphous Al2O3 shell layer, as evidenced by steady-state and transient photoluminescence investigations. The photodetectors demonstrated suppressed dark current and increased photocurrent after capping the Al2O3 layer. Specifically, the ZnO/Al2O3 core-shell microrod photodetector exhibited a photoresponsivity as high as 0.019 A/(W cm-2) with the dark current as low as ∼1 × 10-11 A, and a high I light/I dark ratio of ∼104 under relatively weak light illumination (∼10 μW cm-2). The results presented in this work provide valuable pathways to boost the performance of 1D ZnO microrod-based photodetectors for future practical applications.