Multiwalled carbon nanotubes (MWNTs) are covalently grafted with hydroxyl modified phosphazene, which constitutes a novel flame retardant structure, and introduced into ethylene-vinyl acetate (EVA) copolymer via melt blending. The structure and morphology of the phosphazene-wrapped MWNTs are characterized using Fourier transform infrared spectroscopy and transmission electron microscopy. The grafted phosphazene introduces phosphorus- and nitrogen-containing species onto the surface of MWNTs and thus improves thermal stability of EVA resin and the dispersion of MWNTs in EVA matrix. Thermogravimetric analysis and cone calorimeter analysis reveal that phosphazene and MWNTs produce a synergistic effect on the enhancement of the thermal stability and flame retardancy of EVA. Furthermore, SEM observation indicates that phosphazene accelerates the formation of char residue on the surface of MWNTs. The char residue fills the space in the network structure of MWNTs and glues the MWNTs together. The dense char/MWNTs layers constitute a heat and mass block and therefore a better flame retardancy is observed. (c) 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 4245-4254, 2013