This thesis is exploring interactions of Japanese NGOs to be influential in official foreign aid from outside of the exclusive Japanese decision-making process. Three case studies have been undertaken to examine how Japanese NGOs have developed or adopted various means to exert influence on the government. Japanese NGOs have emerged as powerful actors in foreign aid under a policy of "Kao no Mieru Enjyo (visible Japanese aid)" in the 1990s following some domestic incidents and an international trend in development. However, the Japanese government has maintained a hostile attitude toward NGOs despite its official claim of regarding NGOs as 'partners'. The government's awkward reaction to NGOs comes from Japan's traditional idea of extreme respect for the government and looking down on citizenry. This traditional political culture of "Kan Son Min Pi (supremacy of bureaucracy)" has dominated Japan and that has made the government hostile to powerful outsiders such as NGOs, which may threaten their supremacy. The exclusive decision-making system, "the Iron Triangle", has also contributed to distance NGOs from the government. By this means, an atmosphere between NGOs and the government in Japan has been far from 'partnership'. Against this hostile environment, Japanese NGOs have developed and adopted interactions to exert influence. Various means have been used by each NGO in accordance with each speciality and operation field. The thesis has focused on three areas of Japan's foreign aid - development, anti-personnel landmines and environment - and undertaken three case studies. Four NGOs have been analysed - Japan International Volunteer Center (JVC), Japanese Campaign to Ban Landmines (JCBL), Greenpeace Japan and Friends of the Earth (FoE) Japan. Some NGOs have developed their own interactions and others have been adopted from international partners and authorities. On a whole, they have all crafted these interactions to suit the Japanese political culture. Among several interactions, building international networks and personal relationships with powerful individuals such as politicians have appeared to be most useful. These two interactions work effectively on Japan's reactive and highly personalised aspects of politics, which is reactive to external pressure (Gai-atsu) and rely heavily on the personality and ability of individual leaders. The case studies reveal that Japanese NGOs have exerted influence effectively by making use of these valuable interactions. However, Japanese NGOs are at a crossroad because of high turn-over of staff and a focus-shifting in Japan's foreign policy to sending Self-Defence Forces (SDF) overseas. NGOs also need to obtain solid financial source which is getting difficult after a downturn in the Japanese economy. These will be the issues that Japanese NGOs need to tackle soon in order to be true 'partner'.