This study aims to analyze the role of public-private partnerships （PPPs） in Japan’s foreign aid policy. Recently transnational PPPs have increased to achieve sustainable development in international societies. Yet, Japan seems only to promote domestic PPPs for achieving its national interests. Why does Japan not pursue the use of transnational PPPs? What are the roles and functions of PPPs in Japan’s foreign aid policy? To answer these questions, this article utilizes the Constructivist approach to analyze PPPs in Japan’s foreign aid policy. The research findings include that epistemic communities on Japan’s foreign aid are constituted by PPPs, and that economic interests and the ideas of domestic PPPs influence Japan’s foreign aid as a foreign policy tool.