The article presents the findings of a qualitative research project to explore the emergence of teacher identity of Vietnamese student teachers during a pre-service teacher training practicum placement. There were 9 pre-service teachers employing journal writing as a means to reflect their thoughts based on their observations within the period of 8 week practicum. In-depth interviews were also conducted in week 4 and at the end of the practicum to deeply understand their views of the formation of professional identity. Based on their reflective interviews and reflective journals, the process of forming their teaching confidence, sense of agency and critical consciousness was identified. By reflecting upon their teaching practicum and classroom observations, the student teachers expressed comprehensive aspects of their formation of teacher identity such as their beliefs and perceptions of the responsibilities as teachers, their teaching competencies and their active roles in professional development. Moreover, they also appreciated the experience of writing reflective journals about what they observed and what they did at school in the interaction with experienced teachers, colleagues and school students. The findings suggest recommendations for using qualitative research methods to examine teacher identity in the Vietnamese context and using reflective journals as an important and effective tool for student teachers’ professional development in pre-service training.