Generally ethnicity has been primarily explained through the framework of primordial essence, which is fixed at nationality status. However, this article argues that ethnicity is interactional and continuously (re)constructed by social boundaries, focusing on the ethnicity of North Korean returnees from China as a case study. North Korean returnees who migrate from China to North Korea experience multi-dimensional ethnic boundaries, which are constructed differently depending on time and space. In other words, their ethnicity is not an immutable essence, but is continuously and repeatedly constructed and deconstructed through diverse experience of boundaries. In North Korea s state-building period, political exclusion of persons with relations to China has functioned as an implicit and invisible stigma. During this period, their ethnicity was marked by discrimination and exclusion. However, after the economic crisis, their ethnicity became more explicit and empowered in the relational interaction in socio-political contexts, and they have emerged as a social class gaining economical benefits depending on situation. Therefore, in this sense, this paper demonstrates that the ethnicity of the returnee is constructed through the process of overcoming other-ization both in North Korea and in China. This paper also focuses on reconstruction of ethnicity through the process of migration.