The dependence of shear viscosity, power law constants and extrudate deformation of ENR/Hypalon blends on temperature and rate of shear has been studied. The blend viscosity decreases with increase in rate of shear or shear stress, indicating pseudoplastic behaviour. The viscosity increases with increasing proportion of Hypalon at constant shear rate or shear stress. ENR shows maximum and Hypalon minimum die swell. Blending and fillers reduce die-swell of ENR. Increasing ENR-content increases melt fracture of the extrudate, particularly at hi:gh shear rates. Addition of carbon black filler reduces the surface roughness.