The surface modification of polystyrene (PS) by the blending of 4-acetoxystyrene polymers and their corresponding hydrolysis products, 4-hydroxystyrene polymers, was investigated on the basis of X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), and contact-angle measurements. According to XPS and AFM measurements, when polystyrene-black-poly(4-acetoxystyrene) (PS-b-PAS) or polystyrene-block-poly(4-hydroxystyrene) (PS-b-PHS) was incorporated into PS, the block copolymer was preferentially segregated at the highest surface region of the blend. This segregation increased to a plateau value when more than 5 wt % of either PS-b-PHS or PS-b-PAS was added. The contact angle of the modified PS by PS-b-PAS or PS-b-PHS was slightly lower than that of homopolystyrene, but no further decrease was observed with the blend ratio of the diblock copolymer increasing from 5 to 20 wt %. For a PS/PS-b-PHS blend, the surface atomic concentration ratio O/C increased linearly with the molecular weight of poly(4-hydroxystyrene) blocks in diblock copolymer PS-b-PHS in the range of our study. The different structures of 4-acetoxystyrene polymers and their hydrazinolyzed materials may affect the surface compositions of their blends with PS; among these polymers, PS-b-PHS and PS-b-PAS appeared to be most effective.