Micelle formation of surface active CrIII complexes of the type cis-[Cr(en)2(C12H25NH2)X]2+ (where X = F-, Cl-, Br-) have been studied in n-alcohol and in formamide at different temperatures by conductance measurements. Standard Gibbs free energy changes (Δ Gmic0), enthalpies (Δ Hmic0) and entropies (Δ Smic0) of micelle formation have been determined by studying the variation of the critical micelle concentration (CMC) with temperature. Critical micelle concentrations have also been measured as a function of percentage concentration of alcohol added. It is suggested that alcohol addition leads to an increase in formamide penetration into the micellar interface that depends on the alcohol chain length. The results are discussed in terms of increased hydrophobic effect (solvophobic interaction), dielectric constant of the medium, the chain length of the alcohols and the surfactant in the solvent mixture. © 2006 Elsevier Ltd. All rights reserved.