We report a sonochemical synthesis of homogeneous PtCu3 nanoparticles. Ultra-sonication during reduction in a non-aqueous solution is compared with synthesis under identical conditions in the absence of sonication (to form a Rieke alloy). X-ray diffraction (XRD) measurements suggest that the sonochemical procedure produces an amorphous, uniformly alloyed nanomaterial having a composition consistent with the PtCu3 stoichiometry, while the Rieke alloy is polyphasic. Energy dispersive X-ray (EDX) analysis indicates that the composition of the sonochemically prepared PtCu3 material reflects the nominal values. EDX and XRD analyses also provide evidence for the inhibition of oxide formation on sonochemically prepared PtCu3 nanoparticles, but oxide is readily apparent in the Rieke alloy. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) images of the sonochemically prepared sample show particles with diameters of ∼2 to 3 nm. As-synthesized PtCu3 particles were activated using an electrochemical de-alloying procedure to prepare an oxygen reduction electrocatalyst. The de-alloyed catalyst consisted of a Pt-rich surface layer, over a core indicated as having a Pt3Cu composition. The de-alloyed sample exhibited ∼3 to 6 fold enhancements in oxygen reduction reaction (ORR) activity when compared to commercial Pt catalysts.