Abstract: The influences of nano ZnSn(OH)₆ particles in flexible polyvinyl chloride(PVC) on the flame retardancy and smoke suppression of it were studied by means of limiting oxygen index(LOI), smoke density test, thermogravimetry analysis(TGA) and SEM. The effects of nano ZnSn(OH)₆ on the flame retardancy and smoke suppression are both better than those of the micron ones between 1% and 8% mass fractions of nano ZnSn(OH)₆. The value of LOI increased from 27.1% to 29.5% when flexible PVC was filled with 1% nano ZnSn(OH)₆. The smoke density rating decreased from 88 to 81 when 6% nano ZnSn(OH)₆ was doped. The TGA indicated that the char yields of flexible PVC samples filled with nano ZnSn(OH)₆ were all higher than those of the samples filled with micron ones at 400℃. The char yield of flexcible PVC filled with nano ZnSn(OH)₆ was 4.3% higher than that of flexcible PVC filled with micron ones at 550℃ and was 6.4% higher than that of blank flexible PVC at the same temperature. The SEM proved that the morphology of char formed after combustion of the samples filled with the nanoparticles showed obviously bulgy state with a densified structure, which can inhibit O₂ and heat and combustion gases to go into the PVC bulk. The study of some mechanical properties of the samples verified that the tensile strength and elongation at break were also improved, the best effect was obtained at 4% nano ZnSn(OH)₆.