Two series of thermoplastic elastomer ethylene-octene copolymer (POE) composites and maleated ethylene-octene (POE-g-MAH) with organo-montmorillonite (OMMT) were prepared via melting processing to study their thermal properties and flame-retardancy. The morphology was studied by transmission electron microscope (TEM). The influence of clay dispersion on thermal and flammability properties was investigated by using thermal gravimetric analysis (TGA) and cone calorimeter. TEM showed that agglomerated structure of OMMT within POE matrix but intercalated/exfoliated structures throughout POE-g-MAH matrix. The different dispersion of OMMT resulted in more significant improvements on thermal stability and flame-retardancy in the POE-g-MAH/OMMT nanocomposites compared with POE/OMMT microcomposites. (C) 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013