Thermodynamic and micellar properties of sodium dodecyl sulfate in aqueous solutions of di-, tri-, and tetraethylene glycols were determined employing conductivity, potentiometric, and fluorescence spectroscopic techniques. Intermicellar properties such as effective degree of dissociation, monomer and counter ion concentrations, and activity coefficients were obtained from the mass action model. From the evaluated intermicellar parameters, the hydrophobic and electrostatic contributions to Gibbs free energy of micellization were evaluated. The difference in Gibbs energies of micellization of SDS between water and mixed solvent systems and the results were also interpreted in terms of hydrophobic and electrostatic contributions to the micellization process, Surfactant aggregation numbers (N-agg) obtained from the fluorescence quenching method decrease with increasing glycol content in the solvent composition. The micropolarity of the micellar interior was determined from the pyrene I-1/I-3 ratios,