A one-step method was developed to produce metal nanocomposites from metal alloys under ultrasound irradiation. Systematic investigation of ultrasound effects on various metal particles reveals cavitation-induced recrystallization and oxidation of metals as main factors in the process. The fact that different metals react in dramatically different fashion towards ultrasound irradiation was exploited for the formation of nanoscale composites. Results from the application of ultrasound to formation of nanocatalysts are reported.