Micellization behavior near the critical micelle temperature (c.m) has been studied for polystyrene-block-poly(dimethylsiloxane) (PS-b-PDMS) in a mixed solvent of 1,2-dichlorobenzene/benzyl alcohol, which forms micelles with PDMS as cores. Static and dynamic light scattering experiments have demonstrated the following behaviors. The dilute solution (c congruent to 0.1-4 wt%) shows three different characteristic behaviors depending on the copolymer concentration c. In the concentrated region, the temperature dependence of scattered-light intensity exhibits a large peak just below c.m, which is similar to the anomalous micellization, Detailed light scattering studies have revealed the following: in this concentration region, compact micelles are formed at low temperatures and as the temperature is increased, the micelles change into expanded swollen micelles discontinuously at a certain temperature. This change occurs rather reversibly, and may be explained by a strong condensation of the core due to the decrease in solvent quality with decreasing temperature. This can be a mechanism of the anomalous micellization. (C) 2000 Elsevier Science Ltd. All rights reserved.