Thermoplastic interpenetrating polymer networks (TPIPN''S) were prepared using ethylene-propylene-diene terpolymer (EPDM), high density polyethylene (HDPE), and dicumyl peroxide (DCP) in a laboratory internal mixer. A conventional thermoses blend was also prepared for comparison by curing in a press. The effect of DCP concentration, shear intensity of the mixing, and rubber/plastic composition were studied. The melt viscosity was measured by an instron capillary rheometer, and the tensile tests were done according to ASTM D 1708. The degree of crystallinity was measured by differential scanning calorimetry (DSC). The melt viscosity increased with increasing DCP concentration, and decreased with shear intensity of the mixing presumably due to the formation of the segregated microdomain of the crosslinked EPDM gels. The crystallinity decreased with increasing DCP concentration and slightly increased with increasing shear intensity of the mixing. Increasing DCP concentration, the tensile strength increase and elongation at break had a maximum at particular DCP concentration. Dynamic cure gave somewhat lover tensile strength and elongation int break than press cured samples. But dynamicall cured blends had better processability and superior mechanical properties when compared to linear EPDM/HDPE blends.