Abstract: The distribution data of uranous nitrate and nitric acid in U(NO_3)_4 --HNO_3--H_2O/ 30%(V/V)TBP--kerosene system are determinated systematicly andmathematically descriped in order to exactly calculate distribution coefficients ofthe species in solvents in the stripping column of Purex process. Theconcentrations of the 74 experimental points in equilibrium aqueous phase varyfrom 0.2 to 4N in nitric acid and from 1 to 30 g/1 in uranous nitrate at 25±0.5℃. The data are described mathematically based on pseudo--mass--action equilibriumconstants which are correlated as a function of the concentration of nitrate ionand ionic strength in equilibrium aqueous phase. The values of uranous nitrateand nitric acid in organic phase calculated from the expressions agree withexperimental values with an average deviations of 7.4% and 6.3% for uranousnitrate and nitric acid respectively.