The crystallization process in digital versatile disc (DVD) media was investigated using a time-resolved X-ray diffraction apparatus coupled with in situ photoreflectivity measurement. The time profiles of crystallization were found to be consistent with the changes in photoreflectivity. The phase changes were characterized by the start and end time; 90 ±1 and 273 ± 1 ns for Ge2Sb2Te5, and 85 ± 1 and 206 ± 1 ns for Ag3.5In3.5Sb75.0Te 17.7, respectively. The faster crystallization time in Ag 3.5In3.8Sb75.0Te17.7 is ascribed to its characteristic crystallization process; its X-ray diffraction profile shows a significant sharpening during the crystallization process, whereas the peak width of Ge2Sb2Te5 remained unchanged. The present findings suggest that crystal growth control is another key for designing faster phasechange materials.