Maleic anhydride grafted polyethylene, [2,3-C-13(2)] MA-g-PE, which was synthesized with C-13 labeled maleic anhydride [2,3-C-13(2)] MA in solution, was characterized by C-13 NMR spectroscopy in order to make clear the structure of graft groups. The results reveal that [2,3-C-13(2)] MA-g-PE has succinic anhydride oligomeric grafts with a terminal unsaturated MA ring in addition to well-known saturated succinic anhydride oligomeric grafts and that the former grafts are longer but fewer than the latter.