Micellization process of dodecyltrimethylammonium bromide (DTAB) was studied by using the aromatic probe (benzene) which dissolved in aqueous DTAB solutions. Proton NMR chemical shift measurements of DTAB and DTAB-benzene system showed that benzene molecules solubilized near the micelle-water interface and that the solubilization sites within the micelles are different as the DTAB concentration is passing through 32.0 mM (hereafter we refer this concentration as the second CMC). The change of solubilization sites is also confirmed by abrupt changes of the chemical shifts and relaxation rates of benzene protons in DATB-benzene system at this concentration. It was revealed from the electrical conductivity and viscosity measurements that the solubilization of benzene caused the DTAB micelles to swell out and that the micelles prepared after the second CMC had a greater swelling effect than those prepared before the second CMC. The transition point which reflects the saturation of benzene molecules on the solubilization sites of micelles was observed at one benzene/micellized DTAB mole ratio from the electrical conductivity measurements. Along the different concentration of DTAB solution, this transition point is appeared clearly after the second CMC. From these results it is suggested that the shapes and/or sizes of DTAB micelles of the spherical micelle region prepared after the second CMC are different from those prepared before the second CMC.