Using in situ atomic force microscope (AFM) and Raman spectroscopy, the real-time crystallization properties of Ge 2 Sb 2 Te 5 films at different temperature were characterized. The given AFM topograph and phase images revealed that the structure of amorphous Ge 2 Sb 2 Te 5 films began to change at a temperature of as low as 100°C. When the temperature reached 130°C, some crystal fragments had formed at the film surface. Heating up to 160°C, the size of the visible crystal fragments increased, but decreased at a higher temperature of 200°C. When the Ge 2 Sb 2 Te 5 film was cooled down to room temperature (RT) from 200°C, the crystal fragments divided into crystal grains due to the absence of heating energy. The Raman spectra at different temperature further verified the structure evolution of the Ge 2 Sb 2 Te 5 film with temperature. This work is of significance for the preparation of Ge 2 Sb 2 Te 5 films and the erasing of data.