Ultrasonically devulcanized ethylene-propylene-diene monomer (dEPDM) rubber was blended with virgin ethylene-propylene-diene monomer (vEPDM) rubber. The properties of these blends were investigated and compared with those of blends of ground ethylene-propylene-diene monomer (gEPDM) and vEPDM. The dynamic properties and curing characteristics were studied. The dynamic properties of the uncured blends showed that the gEPDM/vEPDM compounds were more elastic than the dEPDM/vEPDM compounds at a low frequency range, whereas the opposite trend was observed at a high frequency range. In contrast, the dynamic properties of gEPDM/vEPDM vulcanizates were less elastic than those of dEPDM/vEPDM vulcanizates at a low frequency range. The curing characteristics of the blends indicated that an increase in the dEPDM content in the dEPDM/vEPDM blends reduced the scorch time and the maximum torque and increased the minimum torque. A similar but more pronounced tendency was also found for the gEPDM/vEPDM blends. The tensile properties of the dEPDM/vEPDM vulcanizates were much better than those of the gEPDM/vEPDM vulcanizates, indicating the significant benefit of ultrasonic devulcanization. (C) 2004 Wiley Periodicals, Inc.