This article presents a general overview of the South Korean labor market and the main policies for work integration that have been installed recently, and explains how the recent massive influx of North Korean defectors from low social classes has made their work integration in South Korea a worrisome issue. Available data on the work integration of North Korean defectors in South Korea is presented to illuminate the discrimination they face in the primary labor market and the different indicators of their poor work integration. The failure of their work integration is analyzed through a “social capital” framework, with two main approaches: one regarding social capital as a key factor to understand access to the job market, the other relating integration of immigrants, ethnicity, and social capital. North Korean defectors have an especially low social capital due to a weakness of their ties both to persons belonging to the same community and to persons belonging to different communities. The main argument is that there is a close relation between this low level of social capital and the poor achievement of North Korean defectors in terms of work integration. The situation of social exclusion experienced by most North Korean defectors is the result of a process of “disaffiliation” that makes them “social cases” in South Korean society.