The authors have grown nonpolar AlN layers on m-plane ZnO substrates using pulsed laser deposition and investigated their structural properties. The direct growth of AlN on ZnO substrates at 750°C results in the formation of polycrystalline materials due to significant interfacial reactions between AlN and ZnO. On the other hand, m-plane AlN was grown epitaxially on the ZnO substrates by using a GaN buffer layer prepared at room temperature (RT). The full width at half maximum value for AlN 1100 x-ray rocking curve was determined to be 468arcsec. Grazing incidence angle x-ray reflectivity measurements revealed that the heterointerface between AlN and RT GaN is quite abrupt. X-ray diffraction measurements revealed that the in-plane epitaxial relationship is <0001>AlN∥<0001>GaN∥<0001>ZnO. These results indicate that the use of the RT GaN buffer layer makes it possible to take full advantage of small lattice mismatches and the wurtzite structure of the ZnO substrates.