The researcher analysed the language of instruction used by English teacher in the classroom at SMAN 13 Bone. This research aims to find out what language of instruction English teacher use in the English teaching process. In addition, it also aims to investigate the reasons for using the language of instruction in the English teaching process. In this study, the researcher used qualitative methods and used narrative qualitative as a research design. Narrative qualitative research focuses on understanding the experiences of individuals or groups. The subject of this research is the English teacher in class XI of SMAN 13 Bone. The research instruments used were observation and interview. The researcher collected the data by conducting direct interviews with subjects, and documented some important data to support this research. The results of the research collected by the researcher through observation found that the language of instruction used by English teacher in the classroom is Indonesian and English. Then, the results of research through interviews reveal the reasons why the teacher use these languages of instruction. Among them, made students interested in the lesson, providing motivation to students, and based on the existing situation. The language used by the teacher is using two languages, namely Indonesian and English, where the use of these languages can influence students in learning and easy to communicate and, what the teacher wants be achieved. This study also shows that the reason why teacher used English and Bahasa Indonesia in the learning process is based on the aim of attracting students interest and motivating them to learn English. In addition, teacher consider the student language proficiency level in determining the use of English or Indonesian.