In this book the effect of nano sized pre-existing precipitates on UFG structures fabricated by a severe plastic deformation (SPD) process has been studied. The purpose of the present book is to clarify the changes in microstructure, texture and mechanical property during SPD and subsequent annealing processes. For this purpose, several starting microstructures, i.e., the specimens involving pre-existing precipitates with different particle sizes and the as-solution-treated specimens without preciptates, are prepared and then provided to a SPD process. The result indicates that the materials have pre-existing precipitates before the SPD process, it would greatly affect the evolution of UFG structures and the change in mechanical properties during the process.