The data available in the literature and our new experimental data of vapour-liquid equilibrium (VLE), molar excess enthalpies, H-E, solid-liquid equilibrium (SLE) and activity coefficients at infinite dilution, gamma(i)(infinity), for mixtures of different organic solvents with sulfolane are examined on the basis of the group contribution model, modified UNIFAC (Dortmund). New interchange coefficients for various groups/sulfolane contacts, a(mn) and a(nm), of the modified UNIFAC were optimized, The model describes consistently the excess functions G(E), H-E and ln gamma(i)(infinity) of most of the experimental data (VLE and SLE).