This study is to explore the factors affecting the perceptions of teachers and students on Teaching English Through English(TETE). To achieve the goal, this study sets specific objectives as follows; First, is there any difference in the teachers' perception on TETE according to the teachers' variables?, Second, is there any difference in the students' perception on TETE according to the students' variables?, Third, what factors affect to the teachers' and students' perceptions on TETE considering the variables of teachers and students?
200 middle or high school teachers and 500 middle or high school students participated in this study. According to the analysis results, speaking competency and the amount of classroom English are effective in teachers' perception on TETE. Teachers with high speaking competency and more English use in class are tend to perceive positively on TETE. In students' perception on TETE, the competencies in reading, speaking, writing are effective. Also, there are some discrepancies between middle and high school, male and female. Considering both of teachers' and students' variables, teachers' speaking competency, students' perception in TETE's helpfulness and the amount of classroom English are effective in students' perception on TETE. But only teachers' speaking competency is effective in teachers' perception on TETE.