Single-walled carbon nanotube (SWCNT) and multi-walled carbon nanotube (MWCNT) membranes (buckypaper) were incorporated onto the surface of epoxy and bismaleimide (BMI) carbon fiber composites. Their flammability behaviors were investigated by a cone calorimeter. The composites with buckypaper reduced the heat release rate (HRR) by more than 60% peak and smoke generation by 50% during combustion. The effects of different buckypaper on the flame retardancy of epoxy and BMI were compared and discussed. Our research team found that buckypapers acted as an effective flame-retardant shield to dramatically reduce the fire hazards of composites if they survived during fire combustion. Thermogravimetric analyses was used to compare the thermo-oxidation stability of the resins and buckypapers to explain the different effects of SWCNT and MWCNT buckypaper on flammability of epoxy and BMI carbon fiber composites.