Graphene sheets were successfully decorated with ZnS by a facile hydrothermal route, with the purpose of combining their excellent physical and chemical characteristics for fire safety applications in an epoxy matrix. The incorporation of 2.0 wt % ZnS decorated graphene sheets provided fire retardant properties to epoxy resin, testified by the results of microscale combustion calorimetry and cone calorimetry. Moreover, the amount of organic volatiles from epoxy resin decomposition was significantly reduced, and the formation of toxic CO was suppressed, impling a reduced fire hazard. This dramatically reduced fire hazard was primarily attributed to a synergistic effect between ZnS and graphene. During the combustion process, ZnS may act to catalyze carbonization of degradation products. Meanwhile, graphene can function as a physical barrier to absorb degradation products and extend contact time with ZnS catalyst. Degradation products continually collect on the graphene, which serves as a template for the formation of microchar.