After World War II, Japan started afresh as a ‘peaceful state’ under the occupation of the Allied Forces. In so doing, not only Japanese intellectuals but also its public at large found in UNESCO one of the guiding principles that Postwar Japan should be grounded in. As a result, it is in June 1951, prior to its admission to the United Nations and even before the restoration of sovereignty by the Treaty of San Francisco, that Japan was admitted to UNESCO. In light of this historical context, this paper examines how UNESCO was envisaged in Japan during the period from the late 1940s to the early 1950s and what impact UNESCO had on the postwar Japanese society. Particularly, the paper focuses on the UNESCO office in Tokyo, which was established in 1949 and represented by a Chinese educationist, Li Ximou. Scrutinizing interactions between Japan and UNESCO, this paper will argue that UNESCO was commonly understood in Japan as a focal point of the peace movement in the postwar era and it had a significant role in Japan’s reintegration to the international community.