The grafting copolymerization of natural rubber and o-aminophenol was carried out by using two-roll mill machine. The prepared grafted antioxidant, NR-graft-o-AP, analyzed by using Infrared and H-1-NMR Spectroscopy techniques. The thermal stability, mechanical properties, and ultrasonic attenuation coefficient were evaluated for NBR vulcanizates containing the commercial antioxidant, PBN, and the prepared grafted antioxidant, NR-graft-o-AP, and the control vulcanizate. Results of the thermal stability indicate that the prepared NR-graft-o-AP can protect NBR vulcanizate against thermal treatment much better than the commercial antioxidant, PBN, and control mix, respectively. The prepared grafted antioxidant improves the mechanical properties of NBR vulcanizate. (C) 2010 Wiley Periodicals, Inc. J Appl Polym Sci 119: 2461-2467, 2011