Flammability of poly(ethylene-co-vinyl acetate) (EVA), low density polyethylene (LDPE) and their blends represents a great drawback that restricts their applications in wire and cable industry as insulating materials. Magnesium hydroxide (MDH) is a non-toxic flame retardant that its high loading level causes mechanical and processing properties of final composite to become deterirate. In this study in order to imrove flame retardancy and thermal stability of EVA/LDPE/MDH composite, while keeping its mechanical properties, two organo modified montmorillonites (OMMT) with different surface polarity and basal spacing were used. The Samples were prepared via twin screw extruder and with total loading (MDH+OMMT) of 55% and 60% w/w. Results showed that increasing MDH content from 55% to 60% not only didn’t enhance flame retardancy but also resulted in about 30% reduction in elongation at break, while substituting even 2% of magnesium hydroxide with OMMT significantly improved the thermal stability, flame retardancy and tensile strength of the composite. As in comparison with OMMT free sample limiting oxygen index (LOI) increased about 16% and in vertical burning test (UL-94V) dripping was suppressed, furthermore degradation peak in derivative thermogravimetry (DTG) curve 50?C shifted to higher temperatures and tensile strength increased about 30%. Moreover, in differential scanning calorimetry (DSC) test, oxidative induction time (OIT) of OMMT free sample was evaluated about 20 minutes while for the nanocomposites this quantity was more than 140 minutes. According to the LOI and UL-94 tests, synergistic effect was observed between MDH and OMMT on flame retatdant properties, this behaviour could be relared to more char production in the presence of OMMT. In addition, SEM micrographs showed that nanocomposite based on non-polar nanoclay has better distribution than the polar one, with higher elongation at break and thermal stability, and lower tensile strength and viscosity. This behavior could be related to more gallery distance in non-polar nanoclay. Surprisingly, the combination of two organoclays (approximately with the same ratio of EVA/LDPE) brought interesting properties to the nanocomposite. Whereas each of organoclays resulted in intercalated structure, by combination of them semi-intercalated semi exfoliated nanocomposite was obtained, with mechanical and thermal properties . .