AbstractA millable polyurethane prepared from castor oil was blended with natural rubber in a two‐roll mill and sulfur‐cured. It was observed that blending of more than 50/50 (by weight) of the polyurethane with natural rubber was not feasible. Blends were found to have improved tensile modulus and abrasion resistance compared to pure natural rubber. Curing studies on the blends revealed that blending with urethanes enhanced the reversion resistance of natural rubber. The gel contents, measured by Soxhlet extraction using tetrahydrofuran, were above