A pressure-induced amorphous-to-amorphous reversible transformation was revealed in Pr75Al25 metallic glass (MG) using in situ high-pressure synchrotron x-ray diffraction technique. The transition began at about 21 GPa with a similar to 5% volume collapse and ended at about 35 GPa. This transition is reversible with hysteresis. Based on the high-pressure behaviors of Ce-based metallic glasses and Pr metal here, we suggest that the pressure-induced polyamorphic transition in Pr75Al25 MG stems from 4f-electron delocalization of Pr metal which leads to abrupt change in bond shortening. These results obtained here provide new insights into the underlying mechanism of the amorphous-to-amorphous phase transition in metallic glasses and will trigger more theoretical and experimental investigations for such transition. (C) 2013 AIP Publishing LLC.