This paper describes the production of alloy nanoparticles of Co:Fe ratio 65:35 from Aotani solutions in the presence of high power ultrasound (20 kHz). The production of this new type of alloy nanoparticles was performed potentiostatically and galvanostatically at (298 +/- 1) K using a newly designed experimental set-up i.e. a 'sonoelectrode' producing short applied current pulses triggered and followed immediately by ultrasonic pulses. It was shown that cathode efficiencies decreased with increasing current densities and high nanoparticle yields were obtained at low current densities. Morphological and structural studies of the produced nanoparticles were performed by TEM, SEM, XRD, and SAED, and showed that the strongly aggregated Co65Fe35 alloy nanoparticles were predominantly formed, with prevalent body-centered cubic bcc crystalline structure; no redissolution of the nanoaggregates was observed and no separate Fe and Co metallic nanoparticles were produced sonoelectrochemically. The experimental value of the lattice parameter for bcc Co-Fe alloy was 2.85 angstrom and was in excellent agreement with literature values.