A kinetic isotope effect in Pu(V) disproportionation has been observed in nitric acid solution under the effect of power ultrasound with intensity 0.9W·cm–2 and frequency 22 kHz. The isotope separation coefficient for242Pu/239Pu isotopes was found to be 1.0081 at 20°C. Without sonication the k.i.e. was not observed. The rate constant of Pu(V) disproportionation was found to be accelerated under sonication. The rate constant determined was (5.7±0.6)·10–3 12·mol–2·s–1 atl=0.9 W·cm–2,v=22 kHz, [HNO3]=0.5 mol·l–1 andT=20°C. It is supposed that the acceleration of Pu(V) disproportionation and the kinetic isotope effect are due to the activation of plutonoyl groups in the interface between the cavitation bubble and the bulk solvent.