AbstractBlends of nitrile butadiene rubber (NBR) and in‐situ synthesized thermoplastic polyurethane‐urea (PUU) are prepared by a reactive blending method. The PUU is synthesized in‐situ from the polyaddition of 4,4′‐diphenylmethane diisocyanate‐terminated prepolymer with Bisaniline‐M during blending with NBR in an internal mixer. The 1H NMR spectroscopic analysis shows up to 93% conversion of Bisaniline‐M to PUU in NBR/PUU blends. The incorporation of PUU improves the tensile characteristic, tear and abrasion resistance however a temperature dependent softening of amorphous PUU phase diminishes the dynamic‐mechanical behavior of blend vulcanizates. Improvement in physical properties of blends is attributed to good interfacial adhesion between dispersed PUU domains and continuous NBR matrix as seen by TEM.