We have grown transition metal （Fe, Mn） doped GaN thin films on c-oriented sapphire by metal-organic chemical vapor deposition. By varying the flow of the metal precursor, a series of samples with different ion con- centrations are synthesized. Microstructural properties are characterized by using a high-resolution transmission electron microscope. For Fe over-doped GaN samples, hexagonal Fe3N clusters are observed with Fe3N （0002） parallel to GaN （0002） while for Mn over-doped GaN, hexagonal Mn6N2.58 phases are observed with Mn6N2.58（0002） parallel to GaN （0002）. In addition, with higher concentration ions doping into the lattice matrix, the partial lattice orientation is distorted, leading to the tilt orGaN （0002） planes. The magnetization of the Fe over-doped GaN sam- ple is increased, which is ascribed to the participation of ferromagnetic iron and Fe3N. The Mn over-doped sample displays very weak ferromagnetic behavior, which probably originates from the Mn6N2.58.
