A graphene oxide (GO) was produced for upgrading the thermal stability, flammability and decrease in the fire hazards of polystyrene (PS). Cone calorimeter and limiting oxygen index tests were utilized to assess the heat and flame tests of PS nanocomposites. The addition of GO in PS matrix efficiently improved the flame retardancy and reduced the density of carbon monoxide (CO) release, which attributed to the homogeneous dispersal of GO in the PS matrix upgraded barrier effect that reduced peak heat release rate, total heat release and toxic gas evolution during combustion. The characterization implied that the GO nanosheets were well distributed throughout the PS matrix without clear aggregates, leading to outstanding upgrading of thermal stability and fire safety properties. Dynamic mechanical analysis (DMA) showed that both the storage modulus and glass transition temperature (Tg) of PS/GO nanocomposites were significantly promoted related to that of pristine PS. Moreover, PS/GO nanocomposites clearly decreased the amount of flammable volatiles and CO evolved, suggesting suppressed fire hazards of the PS composites owing to proper distribution, physical barrier effect intumescent and loosely structure of char layers. This study provides useful insights into the flammability behavior of polystyrene compounds with layered fillers of GO. © 2019, Central Institute of Plastics Engineering & Technology.