South-East Asia is a densely populated region with a considerable, however, under-prioritized mental health burden. Little is known about the mental health burden and services status in the prisons of the region. We aimed to investigate the individual country-wise prison mental health status in South-East Asian region. We performed a narrative review based on the evidence available in PubMed, Scopus, PsycINFO, Google, and Google Scholar considering the review objectives. We highlighted country perspectives on total population, prison numbers, prisoner numbers, the prevalence of psychiatric disorders and suicide among prisoners, prison mental health services, current challenges, and ways ahead. We discussed the prison mental health of five countries (Bangladesh, India, Indonesia, Nepal, and Sri Lanka). We found overcrowding (131.4%-215.6%) in the prisons, a high prevalence of psychiatric disorders in the prisons (40%-100%), negligible prison mental health services, and a lack of data on prison suicide with some variations among the five countries. Among the countries, Bangladesh has the highest prevalence (66.4%-100%) of psychiatric morbidity with an absence of a mental health system. Prison mental health in tSouth-East Asia is a neglected domain and warrants attention regarding ensuring adequate mental health services to the prisoners as there are high unmet mental health needs and an absence of poorly supported mental health needs.