Polystyrene/Mg-Al layered double hydroxides (LDHs) hybrid nanocomposites were synthesized by emulsion polymerization．The purposed nanocompesites synthesized under different conditions were characterized by the XRD curves．Then the formation conditions of exfoliated PS/LDHs nanocompesites were discussed by the XRD results at low angles．The SEM images were used to observe and analyze the dispersed behavior of the LDHs nanolayers leading to the conclusion that the LDHs nanolayers were exfoliated and well dispersed in these nanocompesites The thermal stability of these nanocomposites was discussed through the TG and DSC curves It was foundthatthe LDHs nanalayers can effectivelyincreasethethermal stabilityof PS．The glass transition temperature nf PS can be enhanced and improved by the well dispersed LDHs nanolayers．The limited oxygen index of the PS/LDH nanocompesites prepared by emulsion polymerization WaS much hish than that of the conventional mixture of PS and nanoo-LDHs at the same LDH content．