This thesis is aimed to explain strategy of Japan’s Official Development Assistance (ODA) as a Japanese foreign policy tool in South Sudan in 2012-2016 in which its assistance aimed to enhance prosperity in South Sudan on Post-Conflict Reconstruction. This study used theories of foreign aid by K.J. Holsti. By using the theories of foreign aid it denoted that Japan’s ODA delivered its aid to South Sudan by using two forms of foreign aid as its strategy, they are technical assistance and grant aid. Japan’s Official Development Assistance delivered its aid to South Sudan for humanitarian motive where it had been as one of the responsibility of Japan to enhance the prosperity in the 3rd countries in which accordance with the ODA Charter 1992 that emphasizes on the recognition on the imperative of humanitarian considerations. The emergence of Japan’s Official Development Assistance in South Sudan began in 2012, one year after South Sudan gained it independence and this country remained undeveloped without adequate basic social services and the living conditions is extremely poor, hence Japan’s Official Development Assistance decided to delivered its aid to South Sudan by several strategies to enhance prosperity in South Sudan.