We have studied the influence of the seed layer on the growth of ZnO nanorods on GaN by vapor deposition and the performance of the p-GaN/ZnO nanorod light emitting diodes (LEDs). The seed layer had a significant influence on the orientation and density of the ZnO nanorods as well as on the current-voltage curves of the devices, while optical properties exhibited a weaker dependence on the seed layer. A uniform and bright yellow electroluminescence was observed in all the devices, while the photoluminescence spectra exhibited a prominent UV emission and a weak green emission.