Blends of NBR and chlorosulphonated polyethylene (Hypalon) containing HAF black were prepared under various mixing conditions. The rheological properties at 130 degrees C were studied at different shear rates using an instron Capillary Rheometer The changes in rheological behaviour with the distribution of carbon black in favour of one and in both phases were studied. With the black predominantly in the Hypalon phase, the blend is less pseudoplastic, accompanied by high Stored elastic energy viscosity die-swell and conductivity interchain crosslinking may be responsible for better properties of the preblend followed by black addition than the blend of black masterbatches. From the rheological study it seems that NBR has a greater affinity towards carbon black than Hypalon in their blend.