Display omitted •Hierarchical interfacial catalysts (Co3O4/Co3O4; Co3O4/NiCo2O4 DSNCs) are designed.•Efficient removal of smoke and toxic gases are obtained after their low additions.•Flame retardancy comparison with reported works strongly affirms their superiorities.•Satisfactory promotions in mechanical property are acquired. The emission of considerable smoke and toxic gases has been the notorious stumbling block on the extended usage of epoxy resin (EP), which often causes serious fire casualties in real fire. Hence, metal organic frameworks (MOFs)-derived self‐sacrificing template strategy is adopted, to prepare metal oxides double-shelled nanocages (Co3O4/Co3O4 and Co3O4/NiCo2O4 DSNCs) as hierarchical interfacial catalysts for suppressing the releases of smoke and toxic gases. With the addition of 2.0 wt% Co3O4/Co3O4 DSNCs, the peak smoke production rate (PSPR), total smoke production (TSP), peak CO production rate (PCOP) and total CO production (TCOP) are reduced by 15.8%, 46.9%, 36.2% and 49.1%, separately. When 2.0 wt% Co3O4/NiCo2O4 DSNCs is incorporated, the PSPR, TSP, PCOP and TCOP are markedly decreased by 40.8%, 55.5%, 46.6% and 48.5%, respectively. These results strongly corroborate the efficacy of DSNCs in suppressing the emission of smoke and toxic CO gas. Additionally, the values of peak heat release rate are reduced by 15.9% and 28.4%, reflecting the inhibited heat release. Flame retardancy comparison with reported works corroborates the prominent merit of DSNCs in inhibiting the smoke release. The clear evidence for suppressed toxic CO and NO gases releases is also acquired from TG-IR test. Profiting from the well-formed nanoflake-polymer interfaces, the mechanical performance is obviously improved. In short, these designed DSNCs possess great efficacy in smoke as well as toxic gases removal and mechanical enhancement of EP. This investigation may provide useful inspirations for designing MOFs-derived hierarchical interfacial catalysts, towards impairing the fire toxicity of polymer.