The paper aims to do a comparative research on foreign social services and cultural understanding of the religious organizations of Korea and of the United States which have been active in Cambodia. The results of the research will be helpful to contribute to develop the support policies of the government authority to religious NGOs and to achieve more effective results in the field of international development by the religious NGOs in Korea. The first part of the paper defines some concepts on community development, international cooperation NGOs, understanding of culture, and foreign social services of the religious organizations. Further the paper makes clear the practical structures of goals and processes of the social service (community development) of religious NGOs which transform the religiocultures of the native population. The second and third parts analyze the religious NGOs of Korea and of the United States. The activities in Cambodia and staff education on the culture of the 12 religious NGOs of Korea are examined to influence the community development or social service which is closely related to cultural change. The third part discusses the activities and staff education of the 7 religious (Christian) NGOs of the U.S. which have practiced the social services in Cambodia. The fourth part compares with the merit points of the religious NGOs of the two countries and discusses the issues of NGO activities in the fields. Finally the paper suggests three points to the NGO authorities in Korea such as financial support of the government authority to the religious NGOs, enforcement of religiocultural education for the staffs of the religious NGOs, and establishment of new department such as world relief service by the denomination basis in the Korean churches.