The present study explored the characteristics of 147 Iranian EFL teachers teaching at senior secondary schools (N = 62) and those teaching in private language institutes (N = 85). Data were collected through a Likert-scale teacher characteristics questionnaire mainly adapted from Borg (2006). Also, for data triangulation purposes, 20 teachers from each group (i.e., 40 in total) were randomly selected and attended a semi-structured interview. The results of Independent Samples t-test indicated, overall, there was a significant difference between the characteristics of senior secondary school teachers and those of language institute teachers. Moreover, the results of Chi-square analysis and content analysis of interviews revealed that EFL teachers of language institutes and senior secondary schools were significantly different regarding some specific characteristics commonly ascribed to successful teaching including good command of aural-oral skills, "being disciplined and punctual", "being open to criticism", "respecting the personality of students", "listening to students' opinions and letting them express themselves", and "showing interest in students and their learning". The findings of the study might prove fruitful for syllabus designers, teacher educators and pre-service EFL teachers as discussed in the paper.