Depleted U3O8 was mechanically activated in suspension with tributyl phosphate (TBP), trioctylamine (TOA) and ethylenglycolmonomethylether (EGME) in planetary ball mill with stainless steel vessels and balls. X-ray diffractograms and IR spectra of the activated solid samples were taken. The radioactivities of 238U and 234Th in the leaching solutions were determined by α/β liquid scintillation spectrometry. The reduction degree of the oxide, the mean crystallite size of U3O8 and U3O7 and the leaching of 238U and 234Th as a result of the mechanoactivation were determined. Higher degree of 238U and 234Th leaching was achieved when mechanoactivation with TBP was performed. No leaching of 238U daughter product (234Th) proceeded at mechanoactivation with TOA and EGME. The role of the solvents complexation ability, milling induced increase of crystal defect concentration and UO2 – ThO2 solid solution formation is discussed. Further studies have to be made to elucidate the potential of the applied approach as a step in spent nuclear fuel processing.