Abstract: Properties of reverse micelle of EO _X PO _Y EO _X type block copolymers and their water solubilization in organic solvent are investigated. The results show that water solubilization and critical "reverse" micelle concentration in p -xylene increases considerably with the amount of 1-octanol added to solvent. It is also revealed that for the EO _X PO _Y EO _X type block copolymers/10wt% 1-octanol/ p -xylene systems,the hydrophilic group (ethylene oxide, EO) plays a crucial role in the process of reverse micelle formation. In addition, the ionic strength of the solubilized solutes influences to some extent the formation of polymeric reversed micelles. When the ionic strength is lower than 1, the addition of electrolytes favors the reversed micelle formation process. An increase in temperature causes an increase of CMC for the copolymers studied. The results indicate that thermodynamically stable micelles are formed spontaneously by block copolymers in octanol-xylene. The formation of micelles in organic solvent is exothermic and entropically unfavorable.