Vietnam has initiated to develop nuclear power since 1994 by stipulating the 10-year nuclear power development master plan (2000-2010) and organizing Vietnam Atomic Energy Commission or VAEC as a core organ responsible for nuclear power development and uses. As 2007, Vietnam Government approved the nuclear power plant construction project. In the first phase, there will be 4 nuclear power plants, which each of them nuclear power plant can produce 8,000 megawatts. Such plants are located at Ninh Thuan province in the south of Vietnam (far from Thailand’s border about 900 Kilometers). Russia and Japan have assisted and supported Vietnam in doing so with budget, construction, legislation and objective plan, human resources development, consulting security standards, and research and development of nuclear power uses. In January 2012, leaders of both Japan and Vietnam signed in the agreement to promote the relation in nuclear power aspect. This agreement will lead Japan to get many advantages. In domestic level, private corporations exporting nuclear technology will be encouraged and expanded in their businesses. Furthermore, Japanese banking business will be also supported in loans to Vietnam government for the construction and wage payment. Since Vietnam has rich natural resources and its legislation is not too strict, Japan has many chances to distribute its goods and nuclear technology to other countries in this region as well. For Vietnam, the cooperation and the assistance in nuclear power development from Japan have caused various advantages. In domestic level, it is the way to stimulate the economy and the investment and develop the infrastructure efficiently. In international level, Vietnam has been accepted from many countries that Vietnam has energy security more than any other country in ASEAN. This will be an opportunity to receive the assistance to develop nuclear power from Japan Russia and IAEA, and also the support in research, technology development, training and resource management, etc. This study has been found that if Thailand still goes on the nuclear power plant project, the cooperation between Japan and Vietnam should be applied appropriately and be accord with National Energy Policy. Such cooperation in the nuclear power development policy creating the coordination among relating agencies is the most important. There are a variety of forms of cooperation from the feasibility study, personnel training in nuclear technology, formulating the operation plans and consulting for rules and regulations relating to nuclear safety, nuclear power plant site selection, promoting education and research about nuclear power management, and 2 supporting each other in the international cooperation of nuclear power especially to make a confidence to members states of IAEA. Consequently, there are the additional suggestions as follows. (1) To set up an organ responsible for nuclear power development and uses clearly and continuously, and prescribe the powers and duties of relating state agencies for representing Thai Government to request for cooperation and assistance from other countries. (2) To select the country which is the leader of nuclear technology and gives the assistance and cooperation to Thailand has to realize national interest significantly, not only the energy security, but also the economy, commercial and investment including the relationship between both countries in the future as well. (3) To educate the development of human resources who work about nuclear power so as to supply for the accidents that may occur in the future. For the impact to Thailand, the success of Vietnam in cooperation of nuclear power plant project with Japan does not affect to Thailand considerably. Thailand still has more advantage over the competition in commercial, industrial and economy such as the readiness of infrastructure system, balance of trade, Free trade system and the strength of private sector. Nevertheless, if Thailand still can not find the solution to have the energy security, it may cause the impact in long term. Consequently, the relating agencies have to consider this point carefully to keep up with the future situation. -