Abstract: The growth of GaN was performed by a Thomas Swan MOCVD on (0001) oriented sapphires. Properties of GaN layers were investigated by photoluminescence, Hall measurement, and optical microscope, respectively. The results indicated that the nitridation condition obviously influenced the photoluminescence properties and electric parameters of GaN films. The GaN films photoluminescence properties could be improved and the background carrier concentrations could be reduced if the nitridation condition was proper. The long nitridation time would influenced the GaN growth mode and promote the 3D growth of GaN, which results in rough surface morphology.