This paper examines the issue of international cooperation in the field of disaster preparedness/reduction by looking into Japan’s assistance to the disaster struck countries after the Indian Ocean earthquake and tsunami in 2004. The objectives of this research are to put in order the theoretical frameworks of international assistance in disaster risk management and by applying the framework to evaluate the effectiveness of Japan’s assistance. Disaster risk management is a continuous process of relief, rehabilitation, reconstruction, disaster reduction and preparedness. However it is usually the relief efforts that catch people’s attention with global media coverage and it is emergency response that international assistance mainly focuses on. As time passes and memories of disaster fade away, international assistance also fades away. Japan with its knowledge and experience of disaster risk management started its term assistance to countries around the Indian Ocean with the overall goal on building better prepared societies to reduce damage and the number of victims in case of future disasters. By examining the activities of JICA, Japan International Cooperation Agency, this paper argues the importance of such cooperation. International cooperation for disaster preparedness/reduction has only a short history with little past academic investigation. Therefore this paper also seeks to clarify the issues and challenges of such assistance.