Japanese foreign economic aid serves as an important factor to promote Japan’s economic growth in the post-war era. In the context of Japan’s economic development，its economic assistance to developing countries is also increasing. After the collapse of Japan’s bubble economy，Japanese government’s official development assistance（ODA）had declined due to the budget constraints. In what way to make full use of limited aid funds effectively has become a very important issue. Although the private flow（PF）may solve the problem of efficiency to some extent，the developing countries that belong to a low-income level is unattractive to the private flow. Through case studies in India and Bangladesh，the article analyzes economic relations between the Japanese government and enterprises and South Asian countries. It is implied that international cooperation should be strengthened to promote the economic development of developing countries.