Pressed films of blends of polystyrene (PS) with ethylene-propylene diene monomer rubber (EPDM) or grafted copolymer of styrene (St) onto EPDM (EPDM-g-St) rubber were examined by small-angle X-ray scattering (SAXS), and scanning electron microscope (SEM). Small-angle X-ray scattering from the relation of phase was analyzed using Pored＇s Law and led to value of interface layer on blends. The thickness of interface layer (sigma(b)) had a maximum value at 50/50 (PS-EPDM-g-St) on blends. The radius of gyration of dispersed phase (domain) and correlation distances a, in blends of PS-EPDM-g-St were calculated using the data of SAXS. The morphology and structure of blends were investigated by SEM.