The influence of attapulgites (ATTs) on cure-reaction-induced phase separation in diglycidyl ether of bisphenol A/poly(ether sulfone) (PES) blends has been studied with scanning electron microscopy (SEM), transmission electron microscopy (TEM), optical microscopy, time-resolved light scattering, and dynamic mechanical analysis at different ATT and PES concentrations. The SEM results show that the incorporation of a small amount of ATT into the blends can change the final phase morphology markedly and affect the secondary phase separation. The TEM results show that ATT particles are pinned down by the interfacial tension at the phase interfaces, and this slows the interfacial motion. In addition, the incorporation of a small amount of ATT particles can improve the modulus because of the increased interfacial interaction of the PES-rich and epoxy-rich phases. (c) 2008 Wiley Periodicals, Inc. J Appl Polym Sci 108: 953-959,2008.