The domain structure and miscibility in the solid state of a series of blends of styrene-butadiene-styrene (SBS) block copolymers and styrene-glycidyl methacrylate (PS-GMA) statistical copolymers with varying molecular weights and compositions were studied using small angle X-ray scattering and dynamic mechanical thermal analysis. Depending on the molecular characteristics of each component, different types and degrees of solubilization of PS-GMA in SBS were found which, in addition to the initially SBS phase morphology, lead to materials with multiphase domain morphologies with differences in size and structure. The degree of solubilization of PS-GMA into the PS domains of SBS was found to be higher for blends containing PS-GMA with lower molecular weight (M-w = IS 100 g mol(-1)) and lower GMA content (I wt%) and/or for SBS with higher PS content (39 wt%) and longer PS blocks (Mw = 19 600 g mol(-1)). Localized solubilization of PS-GMA in the middle of PS domains of SBS was found to be the most probable to occur for the systems under study, causing swelling of PS domains. However, uniform solubilization was also observed for SBS/PS-GMA blends containing SBS with composition in the range of a morphological transition (PS block M-w = 19 600 g mol(-1) and 39 wt% of PS) causing a morphological transition in the SBS copolymer (cylinder to lamella). Copyright (c) 2006 Crown in the right of Canada. Published by John Wiley & Sons, Ltd.563308316