The adsorption thermodynamic for the adsorption of trichloroacetic acid (TCA) from aqueous solutions on composite cation exchanger polypyrrole Th(IV) phosphate has been studied. Thermodynamics of adsorption process was studied considering equilibrium time, pH, cation exchanger doses, trichloroacetic concentration and temperature as controlling parameters. Freundlich isotherm is well fitted for the adsorption results of the trichloroacetic acid. As a result some thermodynamic parameters like Freundlich constants, thermodynamic equilibrium constants (K-o). standard free energy changes (Delta G degrees), and standard enthalpy changes (Delta H degrees) and standard entropy changes (Delta S degrees) have been evaluated. (C) 2011 Elsevier B.V. All rights reserved.