We prepared oxygen-doped and nitrogen-doped Ge-Sb-Te system thin film by RF magnetron sputtering, and investigated its crystallinity and resistivity with several annealing temperature and oxygen and nitrogen doping content. The test phase change device was fabricated to confirm switching characteristics between crystalline (set) and amorphous (reset) phases. The resistance of nitrogen-doped GST changed gradually and oxygen-doped GST shows a rapid resistance change with annealing temperature, since nitrogen-doped GST fee phase was held to high temperature as compared with the phase transition from fee to hep in oxygen-doped GST.