The use of Ge-Sb-Te films for rewritable optical storage is based on the reversible phase change between their amorphous and crystalline states. Study of the crystallization behavior of the films is very necessary to the optimization of film composition and dopants. This work dedicates our experimental investigation on the crystallization behavior of oxygen-doped Ge-Sb-Te phase change films, which were prepared by RF-sputtering. The crystallization behavior of the thin films was investigated using differential scanning calorimeter (DSC). XRD spectra of the films in the as-deposited and heat-treated states show that the films changed from amorphous to crystalline states due to heat-treatment. By measuring the peak temperature of crystallization at different heating rates we calculated the crystallization activation energies and frequency factors. It was found that the oxygen-doped Ge-Sb-Te sample has a higher value of crystallization activation energy than that without oxygen-doping, it is clear that oxygen-doping can improve the crystallization rate of Ge-Sb-Te phase-change material.