Effect of block number in linear styrene-butadiene (SB) block copolymers (BCs) on their compatibilization efficiency in blending polystyrene (PS) with polybutadiene (PB) was studied. Di-, tri-, or pentablocks of SB copolymers as well as their combinations were blended with the mentioned homopolymers; supramolecular structure determined by small angle X-ray scattering method (SAXS), morphology using scanning electron microscopy (SEM) combined with image analysis (IA), and stress transfer characteristics of the blends were chosen as criteria of compatibilization efficiency of the copolymers used. It was proved that the addition of SB BCs led to remarkably finer phase structure and substantially higher toughness of PS/PB blends. Triblock copolymer showed to be the compatibilizer with higher efficiency than diblock, pentablock, and the di/triblock copolymer mixture. (C) 2007 Wiley Periodicals, Inc.