Distribution ratio (DU) and extraction efficiency (EU) of uranium(VI) were investigated using N, N, N', N'-tetrabutyl-3-oxapentanediamide (TBOD) in supercritical carbon dioxide (Sc-CO2). Five diamide derivatives were synthesized; TBOD was found to be the most suitable extractant through solubility data. The composition ratio of uranium(VI) extraction was described as a relation of UO2(NO3)(2)TBOD, through the measurement of DU as the concentration ranges of HNO3 and TBOD. Comparing this with the extractability of TBP, the DU of TBOD was superior to that of TBP in Sc-CO2 by 2 orders of magnitude. The results showed that TBOD could be substituted for tri-n-butyl phosphate (TBP) in Sc-CO2 extraction of uranium(VI). Uranium, fission products (Cs, Cd, Mo, Ba), and corrosion products (Ni, Fe, Cr, Co) were extracted with TBOD in Sc-CO2. Over 90% each of actinides (U, Th) and lanthanides (La, Ce, Gd) were extracted. But, fission products and corrosion products were extracted at a low efficiency of less than 20%, which showed the possibility of selective separation in these metals.