Stability constant and thermodynamic parameters (e.g. Delta H-0 and Delta S-0) have been determined at several temperatures for some multicomponent complexes of varying composition involving poly (acrylic acid) (PAA), poly (vinyl pyrrolidone) (PVP) and poly (ethylene imine) (PEI) in aqueous medium and water-DMSO mixture. It has been observed that the stability constant and thermodynamic parameters of the interpolymer complexes change due to presence of organic solvent in the medium. Some of these observations have been attributed to the change in the degree of solvation of component polymers, reduced hydrophobic interaction and dielectric constant of the medium.