The mean ionic activity coefficient was determined by vapour pressure osmometry in the sodium deoxycholate, (SDC), sodium dode-cylsulphate, (SDS), and sodium tetradecylsulphate, (STS) aqueous micellar systems in a wide range of concentrations and temperatures. Fran these data, we have calculated the Gibbs nonideal energy, the nonideal entropy and partial molal relative properties: Gibbs free energy, entropy, enthalpy and heat capacity at constant pressure. The values obtained are consistent with the current ideas on aqueous micellar systems. From the thermic variation of these functions a different thermodynamic behaviour is observed. This