The influence of the sample morphology and experimental conditions towards the sonochemical dissolution of nanoscale ThO 2 samples in sulfuric acid media is described. Significant sonochemical dissolution rates and yields are observed at 20 kHz under Ar/O 2 atmosphere in dilute 0.5 M H 2 SO 4 at room temperature, contrasting with the generally-reported high refractory behavior for ThO 2. The dissolution of ThO 2 combines the physical effects driven by acoustic cavitation phenomenon, the complexing affinity of Th(IV) in sulfuric medium and the sonochemical generation of H 2 O 2. These sonochemical conditions further allow the observation of the partial conversion of ThO 2 into a scarce Th(IV) peroxo sulfate with 1D morphology resulting from one or both following processes: dissolution/ reprecipitation or formation of an intermediate Th(IV) surface complex.