Carbon black was modified with a long chain unsaturated hydroxy organic acid in presence of dicumyl peroxide and used as a reinforcing filler in NR and NR/BR blend in order to put the acid moiety as a flexible bridge between carbon black particles and the polymer chain for improving processing and vulcanizate properties. Processing behavior and vulcanizate properties were evaluated. The modified carbon black showed improved physical properties along with other optimum vulcanizate properties compared to the control unmodified carbon black.