Abstract: The mechanism of extraction of uranium(Ⅵ) with TBP/kerosene, DHDECMP/kerosene and DHDECMP TBP/kerosene from nitric acid solution is studied. The extracted species is found to be UO 2(NO 3) 2·2TBP, UO 2(NO 3) 2·2DHDECMP and UO 2(NO 3) 2·DHDECMP·TBP, respectively. The extracting equilibrium constants K for these systems are directly measured and their thermodynamic functions Δ H , and Δ S are obtained from the dependence of K upon temperature. The distribution ratio of uranium(Ⅵ) increases with the increase in concentration of DHDECMP, TBP or HNO 3, but decreases with the increase in Gd 3+ concentration or temperature. The addition of oxalic acid depresses the extraction of uranium(Ⅵ), probably dues to its complexion and therefore is beneficial to the stripping of the latter.