The rheological behaviour of polypropylene (PP)/acrylonitrile-butadiene rubber (NBR) blends has been investigated with special reference to the effect of blend ratio, compatibilization and dynamic vulcanization. The morphology of the extrudates and the size and distribution of domains were examined, PP/NBR blends show pseudoplastic behaviour, which is evidenced by the decrease in viscosity with increasing shear rate. The melt viscosity of these blends increased with increasing nitrile rubber concentration and shows negative deviation from the theoretically predicted values. Compatibilization of the blends with phenolic-modified polypropylene (Ph-PP) increases the melt viscosity at low concentrations of Ph-PP. The rheological behaviour of PP/BR blends was correlated with the blend morphology. Dynamic vulcanization has a decreasing effect on die swell values. The effect of temperature on the melt viscosity of the blends was examined and attempts have been made to construct a shear rate-temperature superposition master curve. The melt-flow index values for these blends were measured and have been correlated with rheometer data to develop a master curve for different blend compositions. The morphological analysis indicates that compatibilization of the blends prevents the coalescence of dispersed NBR domains during annealing. (C) 1999 Elsevier Science Ltd. All rights reserved.