Polycrystalline GaN thin films were successfully fabricated on KAPTON flexible substrates at 350℃ by plasma-enhanced atomic layer deposition (PE-ALD). The crystal structure, surface morphology and composition of GaN thin films were characterized by grazing incident X-ray diffraction (GIXRD), atomic force microscope (AFM), scanning electron microscope (SEM), transmission electron microscope (TEM) and X-ray photoelectron spectrometer (XPS). The results show that the thin films are polycrystalline and have a good uniformity, and all the N elements of the as-deposited thin films are in the form of N-Ga bond, indicating that all the N elements are formed into GaN thin films. A little amount of Ga elements exist in the form of Ga-O and Ga-Ga bond to form Ga and Ga2O3. It is indicated that, although KAPTON has good resistance of high temperature, GaN will diffuse back into the KAPTON substrate with a certain distance to form a GaN diffusion layer.