Morphology, interfacial tension, and stress relaxation spectra of immiscible SAN/EPDM blend and its compatibilized blend with SAN-g-EPDM (Centrex) was studied. The results showed that the morphology of the blend had a quick response to added Centrex. In the compatibilized blend with 20-wt% compatibilizer (optimized blend) having a droplet-in-matrix type of morphology, the particle sizes were reduced by a factor of 4. The power-law index of EPDM and SAN obtained 0.33 and 0.53, respectively. With increasing of compatibilizer the power-law index decreased. It meant that at the same amount of EPDM its influence in the blend was increased. Also the cross-over point of G' and G '' curves in the melt of optimized blend decreased which was attributed to increased elasticity. These observations were in good correspondence with the morphological observations. In optimized blend, the number average diameter of EPDM dispersed particles had the lowest value of about 1.8 mu m. The interfacial tension of the compatibilized SAN/EPDM blend was determined from the morphological studies and the relaxation time was calculated using the Palierne and Choi-Schowalter models. The optimized blend showed the least interfacial tension about 0.306 (N/m) which was in agreement with the morphological observations.