Flow behavior of NBR and chlorosulfonated polyethylene rubber (Hypalon rubber) blend has been studied throughout the entire composition range. The effect of preheating of the blend is also studied in order to understand the interchain crosslinking, which has a pronounced effect on the NBR/Hypalon blend properties. Preheated blends, 50:50, thus provide higher viscosity, stored elastic energy, shear modulus, and relaxation time, etc. Lowernvalue of the preheated blends indicates more pseudoplasticity. The shearing accompanied by blend ratio has a predominant effect on the preheated stock due to microgel formation. From the rheological behavior it appears that there is a phase inversion at 50:50 ratio where the maximum amount of interchain crosslinking is expected in the preheated stocks.