The international community has been collaborated for the preservation of Angkor site in the last twenty years. This case which is the heritage conservation through cooperation is an exemplary instance for developing countries and warring nations. For this study, we analyze each of declarations that is adopted through three intergovernmental conferences for the preservation of Angkor and study how the policies of the conservation work. Tokyo Declaration at 1993 is included a pledge of the cooperation from all the countries of the world and an emergency measure and an advice of the policy for conservation on Angkor. Paris Declaration at 2003 is mentioned that the emergency measure for last ten years is effective for conservation of Angkor and emphasized the necessity of practical use of heritage like sustainable development and ethical sightseeing. Angkor Declaration at 2013 assures exertions of last 20 years and convinces that all of activities about Angkor is a commendable precedent to another World Heritages in danger. And it is mentioned a practical use of heritage which is more crucial and new conservation of Angkor.