The purpose of this study is to investigate the relations between states’ behaviors and international institutions, with particular reference to how states create international institutions and how international institutions have influence on state’s policy in regard of non-proliferation of nuclear weapon. The study was conducted through historical review of the negotiations on main international institutions such as NPT and IAEA. In addition, four case studies were conducted to further explore the international institutions’ influence on states’ nuclear policy, including China, Netherlands, the DPRK and India, the four of which composed a spectrum according to whether they are states possessing nuclear weapons and whether they are party to the NPT. The results revealed that, notwithstanding states seek relative power in the anarchic world, states tend to design and create institutions to meet their interest preference when faced with collective action problem. In return, international institutions play a significant role to ensure cooperation by influencing states’ policy. ii