Solutions of polystyrene-b-poly(ethylene/propylene) block copolymer in mixtures of 4-methyl-2-pentanone (a selective solvent of the polystyrene block) and 2-chlorobutane (a good solvent of both copolymer blocks) were studied by static and dynamic light scattering and viscometry, Micelle structural parameters and micellization thermodynamics have been analyzed as a function of the solvent composition. The micelle molar mass decreased as the 2-chlorobutane percentage in the binary mixture increased. However the apparent radius of gyration, the second virial coefficient, and the hydrodynamic radius hardly showed variations. Static light scattering was used to establish the dependencies of the critical micelle temperature on concentration. The standard Gibbs energies, enthalpies, and entropies of micellization have been calculated for the different solvent mixtures from these relationships, The three thermodynamic magnitudes became less negative as the good solvent percentage increased.