An "aircraft" would be useful to do detailed surveys of the surfaces of Mars and Venus. The "aircraft" needs a propulsion engine which can work in the planet atmospheres, mainly consisting of CO2. The purpose of this paper is to assess the feasibility of the CO2-breathing engine using metal fuels for the planet use. The heats of reactions between metals and CO2 were reviewed. Equilibrium compositions and temperatures of the metal-CO2 flames were calculated. It was confirmed experimentally that Al and Mg could burn in CO2.Thermodynamic cycle calculations were carried out to evaluate the performance of a CO2-breathing turbojet engine. With these results, we conclude that it is capable of developing the metal fueled CO2-breathing turbojet engine with a practicable performance.