Flow behaviour of NBR and polyacrylic rubber blends have been studied throughout the entire composition ranges. The effect of preheating of the blends is also studied in order to understand the interchain crosslinking. Viscosity, extrudate swell, power law indices, have been studied as a function of shear rate and blend ratio. The shearing accompanied by blend ratio has a predominent effect on the rheological behaviour of the preheated blends due to microgel formation. From the rheological behaviour it appears that there is a phase inversion at around 50% of NBR, however, preheating does not change this trend.