Abstract: In current literatures, it is the usual practice to correlate the pseudo-mass-action equilibrium constants as a function of total ionic strength. At present, these relations are extensively used as the basis of mathematical modelling to calculate the distribution coefficients. However, the correlations obtained by various authors, although based on the same principles, gave results quite different from each other.In order to overcome this shortcoming, aggregative variables RU, RH are being introduced in our work, based on the pseudo-mass-action equilibrium expressions. RU,, RH can be readily calculated from the equilibrium concentrations of uranyl nitrate and nitric acid in aqueous phase with empirical expressions given by the authors. The values of concentrations of uranyl and nitric acid in the organic phase can be finally calculated with RU and RH.The values of concentrations of uranyl nitrate and nitric acid in organic phase calculated from the expressions agree with experimental values with an average deviation of 8.9% and 11.3% for uranyl nitrate and nitric acid respectively.These expressions are better fitted for more than 200 groups of distribution data published in the literature.