Some semitheoretical models for the determination of physicochemical constants of di-2-methylnonylphosphoric acid (DMNPA) and di-2-ethylhexylphosphoric acid (DEHPA) are evaluated. Dissociation constants (pK(a)) for the two dialkylphosphoric acids have been estimated by using the modified Hammett equation. The pK(a) values are also estimated by an interpolation method based on the Born equation. Distribution equilibrium between water and some kinds of organic solvents has been studied for DMNPA and DEHPA. The dimerization constants (K-2) and distribution constants (K-D) for the two dialkylphosphoric acids are predicted by using Leggett equation and Kamlet-Taft solvatochromic parameters. The linear solvation energy relationship model can be applied to the approximation of log K-2 and log K-D for DMNPA and DEHPA in different organic solvents.