This paper describes the concept of an air/fuel integrated thermal management system, which employs the VCS (Vapor Cycle System) for the refrigeration unit of the ECS (Environment Control System), while exchanging the heat between the VCS refrigerant and the fuel into the engine, and presents a feasibility study to apply the concept to the future all electric aircraft systems.The heat generated in an aircraft is transferred to the ECS heat exchanger by the recirculation of air and exhausted into the ram air. While some aircraft employ the fluid heat transfer loop, the transferred heat is exhausted into the ram air. The usage of ram air for the cooling will increase the ram drag and the fuel consumption, thus, less usage of ram air is preferable. Another source for heat rejection is the fuel. The heat exchange with the fuel does not worsen the fuel consumption, thus, the fuel is a preferable source. However, the heat exchange between hot air and fuel has a potential fire risk, so it would be difficult to apply the air/fuel integrated thermal management in the conventional ECS, which generates hot air in the ACS (Air Cycle System). The VCS uses inert refrigerant and reduces a potential fire risk even through exchanging the heat with the fuel; thus, it is suitable for the air/fuel integrated thermal management.The authors conducted thermal balance analysis of the proposed integrated thermal management system and suggest it will improve fuel consumption both in hot and standard weather conditions.