Light emitting diodes (LEDs) consisting of p-GaN epitaxial films and n-ZnO nanorods have been fabricated and characterized. The rectifying behavior and emission spectra were strongly dependent on the electronic properties of both GaN film and ZnO nanorods. Light emission under both forward and reverse bias was obtained in all cases, and emission spectra could be changed by annealing the ZnO nanorods. The emission spectra could be further tuned by using a GaN LED epiwafer as a substrate. Both forward and backward diode behavior has been observed and the emission spectra were significantly affected by both the properties of the GaN substrate and the annealing conditions for the ZnO nanorods.