The hydrogenation process of aluminum, especially pulverization of aluminum prior to the hydrogenation reaction was investigated by in situ synchrotron radiation X-ray diffraction measurements at high pressure and high temperature. Changes in the crystal grain sizes during the hydrogenation process were observed using the angle dispersive method, while weak Bragg peaks from aluminum and AlH 3 with small X-ray scattering factors were detected using focused monochromatic X-rays as the incident beam. The in situ measurement system monitored the pulverization of aluminum at several pressure-temperature conditions where AlH 3 was thermodynamically stable.