The purpose of this research is to analyze the impact of changing Thai - U.S. relation between 1920 - 1963 upon Thailand's political, military, economic, social and diplomatic policies and practices. The main interest of this research is to analyze critically the development of the relation from the starting points to the end of Marshal Sarit Thanarat era and to show the trends of the foreign relations of these two countries. In order to show the evolution of the Thai - U.S. relations, the researchers have divided the work into 6 different chapters according to each period as followed :- (1) - The introducing chapter describes the formation of the problems, purpose of the study, the scope, research processes and the data used in the research and the benefitial suggestions in doing research. Chapter 1 studies the starting point of the Thai - U.S. relations from 1920 to beginning of World War II. It is the period when Thailand was negotiating the unfair treaties on the extra territoriality of Siam. Chapter 2show the develops of closer relationship between Thai - U.S. relation during World War II. This has an impact on the Thai foreign relations leaning towards the western world especially towards the United States after World War II. Chapter 3 gives the description of the changing of Thai foreign policy from neutrality to the pro-western world especially towards U.S.A. This was due to the facts that Thailand wants to keep up with her national interest. Thus this was the new era of closer cooperations with the western worlds especially with the United States in order tocontain the communist interventions and penetrations. Chapter 4 shows the Thai - U.S. relation during Marshal Sarit Thanarat period. The relations during this period were not as smooth as previous periods due to the changing in the political environments of the world especially Thailand neibouring countries. Marshal Sarit Thanarat commenced his era in foreign policy with independence from foreign inter-ventions. But due to the political crisis inher neibouring countries and the fear of communist penetration into Thailand made the Premier to change his foreign policy into a closer relation with the U.S.A. Chapter 5 summerizes the Thai - U.S.relations during the past 43 years.
