This study examines bilingual identity of Vietnamese ethnic minority students as reflected in their language practices, language beliefs and language management. It also focuses on factors related to ethnic-cultural factors, social factors, interaction and investment that influence their bilingual identity. Data were obtained from multiple semi-structured interviews conducted with a group of college-age students. Findings suggest that the students, in practising and managing their languages while being informed by their language beliefs, configured their identity as a process in which both preservation of ethnic identity (maintenance) and construction of mainstream identity (transformation) were active. It is argued that there can be a harmonious coexistence between maintenance and transformation in the same individual under certain social circumstances. For some students however, the transformation tendency inclined to become stronger, and that raises the question of their maintenance of L1 and ethnic identity in the long run. As ethnic-cultural factors seemed to be the most salient influence on the students' maintenance orientation, implications for optimising the role of ethnic-cultural factors, that are critical for protection of endangered minority languages, are suggested.