The effects of the block length and block number of linear styrene-butadiene (S-B) block copolymers on their compatibilization efficiency in blending polystyrene with polybutadiene were studied. For this purpose, two sets of model S-B copolymers and both homopolymers were prepared by anionic polymerization. Diblocks, triblocks, or pentablocks of S-B copolymers were blended with these homopolymers, and the structures and some end-use properties of the blends were determined. The supramolecular structure (determined by small-angle X-ray scattering), morphology (determined by transmission and scanning electron microscopy), and stress-transfer characteristics (impact and tensile strengths) of the blends were chosen as criteria for the compatibilization efficiency of the copolymers used.