Effects of E/P ratio of the EPDM rubber on the flow behavior and morphology of the crosslinkable polyethylene and EPDM blends have been studied as a function of shear rate and processing temperature. High-E/P-ratio EPDM rubber exhibits high viscosities within the temperature range studied but the extrudate swell is higher for the low E/P ratio EPDM. Shear modulus, stored elastic energy and flow activation energy are higher for high E/P ratio EPDM but relaxation time is higher for low E/P ratio EPDM. At a particular blend ratio these rheological parameters show a change in their pattern. This point of change in pattern occurs at a lower level of EPDM having a high E/P ratio; this suggests an early phase inversion as corroborated by the SEM studies. Melt fracture occurs to a larger extent for the low E/P ratio EPDM in its blends with XLPE.