The thermal degradation of two epoxy resin/carbon fiber composites which differ by their volume fractions in carbon fiber (56 and 59 vol%2) was investigated in cone calorimeter under air atmosphere with a piloted ignition. The external heat flux of cone calorimeter was varied up to 75 kW.m -2 to study the influence of the carbon fiber amount on the thermal decomposition of those composites. Thus, main parameters of the thermal decomposition of two different composites were determined such as: mass loss, mass loss rate, ignition time, thermal response parameter, ignition temperature, critical heat flux, thermal inertia and heat of gasification. As a result, all the parameters that characterize the thermal resistance of composites are decreased when the carbon fiber volume fraction is increased.