Industrialization and modernization in urban areas, and natural disasters and market variability in rural areas, have resulted in the recent acceleration of an outflow of rural migrant workers in the Vietnamese Mekong Delta to big cities in the hopes of improving their livelihoods. However, this process has been associated with many vulnerabilities and unsustainable livelihoods for out–migrants because they are ill–prepared for their new environments. This issue highlights a crucial need for adaptive capacity assessments that can contribute to the sustainable development of livelihoods of such vulnerable migrants. A household survey covering 100 respondents as well and interviews with a panel of key informants were conducted for this study to measure the adaptive capacity of migrants using a sustainable livelihoods framework. The study found that the adaptive capacity of out–migrants was 0.306. Numbers of primary laborers and their dependents, migrants’ education, and land ownership were factors affecting income per capita, which is the main indicator of adaptive capacity. For sustainable livelihoods to be more achievable, improvements in access to education and job creation need to be simultaneously considered. In particular, more attention should be paid to vulnerable rural groups such as the poor, children accompanying their parents during the out–migration process, and people affected by development processes and policies.