Currently, there is a rapid increase in the international migration around the world. This may be due to various reasons, such as political situation in their home countries (refugees or asylum seekers), job or business opportunity, works, studies, or to start and/or to live with families. In 2017, it was found that approximately one fourth (25.7%) of international migrants resided in overseas more than 3 months with the purpose of working or starting families, so-called “Expatriates (Expats)”, accounted for 0.9 of the world population (7.6 billion). In Thailand, according to the data of Foreign Workers Administration Office, Department of Employment, Ministry of Labour (as of October 2019), there were foreigners who obtained a working permit in the country totally 3,028,000 people. Most of them were migrant workers from Cambodia, Lao PDR, Myanmar, and Vietnam (CLMV), which were 2,748,189 people. When considering only skilled workers (excluding CLMV workers), there were 166,896 people (6.07%). More than half (92,860 people; 55.64%) of these skilled workers lived in Bangkok, while the rest were scattering in other regions (74,030 people; 44.36%). Of those who lived in other regions, 7.19% (5,330 people) lived in the north-eastern region. However, this figure was the record of foreigners with a work permit only. There would have been many foreigners that come in and out as a tourist and temporarily stay in the country by marrying Thai women or living with Thai partners, whom Thai people called “Keui Farang” -- which literally means “Caucasian son-in-law” – with the term “Farang” referring to Caucasians. Although there are increasing trends of international migration globally as well as substantial numbers of Expats in Thailand, there are limited studies to investigate health and well-being or health related issues among these people. There may be some studies about neighboring migrant workers; however, the studies about Expats, particularly those come from Europe or America who have families in Thailand are very scarce. This study aimed to explore the situation of Expats’ health, especially health service utilization, health insurance, and unmet need. This information is very important and useful for health systems design in responsive to health need of this group of people in Thailand. Methods This study employed a mixed method design, focusing on Expats who came to have families and live in the northeast of Thailand only or son-in-law foreigners (not only westerners as there might have been male Expats from other places e.g., Middle-eastern, Asian, or Asia-pacific countries). The purposively selected study areas comprised three provinces: Nong Bua Lam Phu, Udon Thani, and Khon Kaen. Quantitative data were an analysis of 43 files (Health service data of public hospitals that are annually submitted to the Health Data Center of the Ministry of Public Health (MOPH)). Also, the health survey among son-in-law foreigners by using the survey questionnaire (68 questions) adapted from the Health Welfare Survey questionnaires of the National Statistics, which consisted of 83 respondents. Qualitative data included the reviews of literature conducted in Thailand and elsewhere, and the in-depth interviews and focus group interviews purposively conducted among 42 participants. interviewees comprising 6 MOPH policy makers, 4 representatives from other ministries that deal with foreigner-related work (Ministry of Justice, Ministry of Foreign Affairs, Ministry of Social Development and Human Security, and Immigration Bureau of the Royal Thai Police Headquarters), 1 NGO staff, 3 academics, 1 Deputy Director of a Provincial Health Office, 1 Director of a District Health Office, 11 public health officers, 4 registered nurses, 2 staff from the international affairs unit of a private hospital, and 9 expatriates comprising 6 different nationalities (2 French, 2 English, 1 Swedish, 1 American, 1 Australian, 1 Swiss and 1 Canadian).