The effects of ultrasonic irradiation on morphology and compatibility of polypropylene (PP)/ethylene-propylene-diene terpolymer (EPDM) blends were examined. Results show that ultrasound irradiation lead to stable morphology with reduced disperse phase size. Dynamic rheological analysis indicates the more homogeneous internal structure of PP/EPDM blend is obtained with ultrasonic irradiation. Increase the residence time of the blends in the ultrasound irradiating zone, the structure of the blends get even more homogeneous. The interfacial tension between PP and EPDM melts obtained from the Palierne emulsion model decreases with applying Of ultrasound irradiation and increasing of residence time. The glass transition temperatures of PP and EPDM phase become closer to each other with ultrasonic irradiation. FTIR analysis indicates in situ copolymers formation between PP and EPDM happens with ultrasound irradiation and the copolymer consequently acts as compatiblizers for the blend. (c) 2005 Published by Elsevier Ltd.