Abstract: Poly(tert-butyl acrylate-b-styrene) (PtBA-b-PS) block copolymer was synthesized by radical telomerization of tert-butyl acrylate (tBA) and atom transfer radical polymerization of styrene. Poly(acrylic acid-b-styrene) (PAA-b-PS) amphiphilic block copolymers were obtained by selective hydrolysis in the presence of trifluoroacetic acid, which were characterized by 1H-NMR, FT-IR and GPC. The amphiphilic block copolymeric micelles were prepared by dialysis against water. Laser particle size analyzer and transmission electron micrograph (TEM) measurements were used to examine the morphology and the size of the micelles. The effect of the molecular weight of PS block on the size of the micelles was investigated. Results showed that PAA-b-PS amphiphilic block copolymers formed spherical micelles with average size of 140-190 nm, and the size distribution was narrow. The average size of micelles increased with the molecular weight of PS block.