Maleic anhydride was chemically attached to depolymerized natural rubber by a photochemical reaction. The product Carboxy Terminated Liquid Natural Rubber (CTNR) was characterized by H-1-NMR, IR, GPC, and TGA. The efficiency and permanence of CTNR were compared with conventional plasticizers in NBR vulcanizates. This polymeric plasticizer was found to be less volatile and more resistant to oil extraction. The vulcanizates showed improved aging resistance compared to vulcanizates containing conventional plasticizers.