Ethylene vinyl acetate (EVA) copolymer was filled with aluminum hydroxide (ATH) with three different sizes of 1.8, 1.2 and 0.8 mu m in various volume fractions. The effect of interfacial compatibilizer on the properties of the composites was studied by morphology observation, dynamic mechanical analysis, tensile and flame tests. The results illustrated that the incorporation of functionalized polyethylene combined with dicumyl peroxide (DCP) and the silane coupling agent led to a pronounced improvement in the tensile strength compared to the composites with ATH untreated or treated by silane coupling agent alone. It was found that good dispersion and interfacial adhesion between the ATH particles and the matrix can improve the flame properties of composites. The particle size has a great effect on the flammability of the EVA/ATH composites. ATH with smaller particle size can increase the LOI value and improve the UL-94 flammability of the composites.