This paper sheds light on the process and reasons behind Harry S. Truman's suggestion for the Far Eastern Commission (FEC) to permit basic research and academic instruction of nuclear physics in Japan in 1946 and acceptance the FEC's decision that prohibited any research in 1947. This paper argues that Truman administration planned to relax the restrictions from the various perspectives, such as the international negotiation for controlling nuclear energy at the United Nations and the policy in occupied Germany. After facing oppositions in FEC, however, Truman dropped his suggestion and sought for just the multilateral decision by the FEC to share responsibility of its restriction.