The construct of teacher efficacy is considered to be one of the factors that have an effect on beliefs, judgements and practices of teachers as well as performances of students in an educational process. With the aim of exploring the factors affecting teacher efficacy perceptions of pre-service teachers, the present study used a mixed methods design, and collected the relevant data from 113 participants majoring in ELT at a state university in Turkey. The analysis of the data yielded a moderate level of overall perceived teacher efficacy in the sample, and the findings of the focus group interviews with 22 participants revealed four main factors that affected the development of teacher efficacy perceptions either positively or negatively: ELT education, practicum experiences, perceived language proficiency, and affective states, out of which practicum experiences had the greatest effect on the perceived teacher efficacy. Accordingly, certain implications were presented concerning language teacher efficacy.