The growth mechanism and characteristics of the nonpolar GaN/ZnO heterostructure grown on the r-plane sapphire substrate by using molecular beam epitaxy were studied. The crystal interaction between GaN and ZnO epitaxial layers was clarified by using transmission electron microscopy and X-ray diffraction. A new epitaxial relationship of ZnGa2O4 (220)//GaN (101̅3̅) in the normal surface direction was obtained in the GaN/ZnO heterostructure. It was believed that the formation of ZnGa2O4 (220) was due to the recrystallization of the ZnO layer with Ga atoms, which in turn resulted in the formation of semipolar-oriented GaN. In addition, the main optical transition in the GaN/ZnO heterostructure was attributed to the existence of the interface states and new ZnO:(Ga,N) alloys.