A novel amphiphilic diblock copolymer having sulfonic acid groups in its hydrophilic chain with poly(diethylsilacyclobutane) as a hydrophobic segment was synthesized by living anionic polymerization followed by treatment with 1,3-propane sultone. The polymer backbone with a degree of polymerization of 18 (hydrophobic):37 (hydrophilic) was synthesized, and three kinds of diblock copolymers with different degrees of sulfonation (alpha = 0, 0.50, 0.81) were prepared as sodium salts. The surface tension of aqueous solutions of highly sulfonated polymers as including the alpha = 0 (all carboxylic acid) polymer did not decrease with polymer concentration. The solutions did not show foam formation even after vigorous shaking, and almost no adsorption of polymer molecules was observed at the air/water interface by X-ray reflectivity measurement. However, micelle formation with a radius of 140-200 Angstrom was confirmed by dynamic light scattering and small-angle X-ray scattering experiments. Hence, this polymer showed ''micelle formation'' without ''Gibbs monolayer formation'' in water. The surface tension decrease in 0.5 M NaCl aqueous solution was also small, but adsorption of polymer was observed by X-ray reflectivity in addition to formation of foam by shaking. The strong ionic character of this novel class of amphiphilic polymer is thought to be the origin of this curious behavior.