Numerous undocumented and uninsured foreigners living in Japan have faced barriers when trying to obtain appropriate healthcare services, which have occasionally led to issues with unpaid medical bills to medical institutions. Although information on health and socioeconomic status is essential to tackle such issues, relevant data has been unavailable due to difficulties in contacting this population. This study involved a cross-sectional survey using questionnaires concerning the general demographic characteristics, socioeconomic status, health profiles, information access, and knowledge/attitude/practice of health insurance of Thai nationals living in Japan. The study participants included Thai nationals who lived in Tokyo and the surrounding prefectures. The survey was conducted mainly at public religious events from September 2022 to December 2022. Overall, the questionnaires were obtained from 84 participants, though 67 participants were included in the final analysis after excluding missing variables. There were participants with unspecified visa status (32.8%) and uninsured status (40.3%). Among them, 86.4% expressed positive attitudes towards health insurance. However, multivariate multivariable regression analyses revealed the low insurance practice status among the unspecified visa group (aOR, 0.02; 95% CI, 0.00–0.13). Overall, the results reveal limited access to healthcare services in subgroups of Thai immigrants in Japan.