A structural defect of incipient edge dislocation in epitaxial wurtzite GaN film is confirmed in this paper. The defect is observed as an isolated (1120) boundary segment within one large perfect crystal area by high-resolution electron microscopy. It has the local atom configuration as a part of (1120) high-energy like-atom bonding boundary together with two 1/6［1120］ partial edge dislocations at its two ends. The origin of the defect is explored from the mechanism of epitaxial growth.