Teachers’ professional identity has been the topic of abundant research in recent few decades. It has been defined as the knowledge a teacher has of himself/herself in teaching contexts, and relationships that manifest themselves in practical professional undertakings. This study aimed at investigating the factors that most likely influence identity construction of Iranian EFL teachers. In this convergent mixed-method study, the data in the quantitative and the qualitative phases were collected, respectively, through a questionnaire and semi-structured interviews. The participants of the study were 75 English language teachers who teach in Iranian public schools. The quantitative data were analyzed by means of SPSS and the qualitative data were analyzed manually through thematic analysis. The findings showed that the majority of the participants believed that gaining experience has been the most determining factor in construction of their identities as EFL teachers. Other factors such as inspiration of previous teachers, peer learning and particularly the university programs, however, have been less effective or have had little effect in this regard. This study has implications for ELT stake-holders.