A novel flame retardant (SPDH) containing phosphorus was synthesized through the reaction of 10-(2, 5-dihydroxyphenyl)-9, 10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO-HQ) and synthesized intermediate product 3, 9-dichloro-2, 4, 8, 10-tetraoxa-3, 9-diphosphaspiro(5.5)undecane-3, 9-dioxide (SPDPC). The structure and properties of SPDPC and SPDH were characterized by Fourier transform infrared spectroscopy (FTIR), nuclear magnetic resonance (NMR) spectroscopy and thermogravimetric analysis (TGA). After blending with poly(ethylene-co-vinyl acetate) (EVA), the flame-retardant properties of EVA/SPDH composites were estimated by cone calorimeter, limited oxygen index (LOI) and UL-94 tests, whereas the thermal stabilities were investigated using TGA. The morphological microstructure of the char formed by EVA/SPDH composite after combustion in cone calorimeter was investigated by scanning electron microscopy (SEM). The results indicate that the flame retardant and thermal stability were improved by incorporation of SPDH. The rich foamy char layers were observed from the residues after combustion in a cone calorimeter, which exactly benefits the improvement of thermal stability and flame retardant property of materials. Copyright © 2010 John Wiley & Sons, Ltd.