The optical transparency, thermal resistance, intermolecular interaction, and mechanical properties of poly(styrene-block-butadiene-block-styrene) (SBS), which were modified by blending with crystalline polypropylene (PP) or amorphous polystyrene (PS), were analyzed. The dynamic mechanical test indicated that the PP exhibited an intermolecular interaction with SBS and PS was compatible with SBS. The optical properties indicated that the direction of the light was changed due to the difference between the refractive indices of SBS and the added modifiers. Additionally, refraction and reflection occurred at the interface, reducing the transparency of SBS. The thermal resistance of SBS clearly improved upon modification by the addition of crystalline PP polymer. The thermal treatment increased the tensile strength and the elongation at breakage of modified SBS by reducing the internal stress, which was generated during the blending process. (C) 2009 Wiley Periodicals, Inc. J Appl Polym Sci 116: 172-178, 2010