To study the contributions of both the Vietnamese in Thailand and Thai people to the liberation movements in Vietnam during the First Indochina War and how the support from Thai people influenced the relations between Thai people and Vietnamese during this period. The study adopted a qualitative research method. Research techniques consisted of documentary research and interviews. Moreover, case studies were carried out in Nakhon Phanom and Udon Thani, where there was a large Vietnamese community and where the patriotic movements took place, in order to collect relevant data. The study finds that although the changes in Thai government from that of Prime Minister Pridi Banomyong (1946-1947) to the one led by Prime Minister Phibun Songkhram (1948-1954) had negative impacts on the Vietnamese community in Thailand, the Vietnamese community there still played a crucial role in supporting the war efforts in Vietnam. Moreover, it is undeniable that the patriotic movements of the Vietnamese received a lot of help from both Thai leaders, especially those in the Seri Thai group, and Thai people in the northeast. Furthermore, despite Phibun’s strict control of the Viet Kieu, relations between the Thai and Vietnamese were still good. This stemmed mainly from “Viet-Thai friendship” activities of the Vietnamese and also from Ho Chi Minh’s effort to promote friendship between the two peoples during his stay in Siam in the late 1920s. This partly accounted for the love and protection of many generations of Siamese for Viet Kieu. Siam became a place of providing human forces and was also a bridge for Vietnamese revolution to penetrate Vietnam.