Background/purpose: Although studies on teacher research are becoming more common in English language teaching (ELT), there is still a lack of understanding regarding how university lecturers shape their research identities. Using Ecological systems theory and Self-determination theory, this study examines the construction of research identities among Vietnamese lecturers of English as a foreign language (EFL). Particularly, this study explores how the lecturers perceived the role of research and the ecological factors that influenced their research identities. Materials/methods: Data were collected from document analysis and semi-structured interviews with 18 EFL lecturers across different career stages (early, mid, and late) through a phenomenological research design. Results: The findings from this study highlighted the complexities and dynamic nature of research identities among Vietnamese EFL lecturers within the context of national education reform. Research was seen as an important facet of EFL lecturers' professional development (PD) because it enhanced their teaching practices, contributed to career advancement, strengthened professional relationships, promoted autonomy, and fostered reflective teaching practices. Additionally, the study indicated that the construction of research identities among these lecturers was influenced by diverse ecological factors (e.g., national foreign language projects, lack of managerial and collegial support, lack of financial incentives, lack of research resources, time constraints, personal responsibility, and professional recognition). Conclusion: This study demonstrates the importance of a phenomenological approach and contributes to the expanding body of empirical studies on the construction of EFL lecturers' research identities. It also offers insights that may be applicable in other global contexts.