This study aims at exploring the professional identities of six ELT students through the lens of critical incidents. For the sake of this aim, six ELT students took part in this research at an Anatolian High School in 2018-2019 spring semester. The teaching practicum process was conducted from April to mid of May 2019, once a week over six-week practicum. The main data collection of this study was the Critical Incident Questionnaire (CIQ). Additionally, two questions were asked to the participants to evaluate their actual and designated professional identities. The first question was answered before the practicum and the second one was answered at the end of the practicum process. The results showed that some internal and external factors influenced their professional identity. Additionally, it was found that critical incidents could be used to spot the changes in the participants' professional identity formation processes. Results of the study indicated that not only negative but also some positive critical incidents contributed to the participants' professional identity formation. As a result of the encountered incidents that influenced their formation of identities, it was observed that the actual identities of four students changed from positive to negative at the end of the process. Correspondingly, the findings of this study put forward that how the participants explored their identity formation process through the critical incidents.