The archival life of phase-change memories (PCM) is determined by the thermal stability of amorphous phase in a crystalline matrix. In this paper, we report the effect of ion beam irradiation on the crystallization kinetics of amorphous Ge{sub 2}Sb{sub 2}Te{sub 5} alloy (GST). The transition rate of amorphous GST films was measured by in situ time resolved reflectivity (TRR). The amorphous to crystal transformation time decreases considerably in irradiated amorphous GST samples when ion fluence increases. The stability of amorphous Ge{sub 2}Sb{sub 2}Te{sub 5} thin films subjected to ion irradiation is discussed in terms of the free energy variation of the amorphous state because of damage accumulation.