Rare earth metal Tb was employed as the catalyst to prepare GaN nanostructures. GaN nanorods were synthesized through ammoniating Ga2O3/Tb films sputtered on Si(111) substrates. Results of X-ray diffraction (XRD) and Fourier transform infrared spectrum (FTIR) indicate that the prepared nanorods are hexagonal GaN. Observations of scanning electron microscopy (SEM), transmission electron microscopy (TEM) and high-resolution transmission electron microscopy (HRTEM) show that the GaN nanorod is single-crystalline in structure with 80~200 nm in diameter and several tens of microns in length. The growth mechanism of GaN nanorods was also discussed briefly.