This study examines the authentic leadership practices in Islamic secondary schools in East Kalimantan, Indonesia and elaborates on leadership styles for teacher performance. A survey method using quantitative approach was applied in this study. Descriptive statistics and t-test were used to analyze data. This study assigned 30 principals and 60 teachers as the respondents. In addition, 5 kinds of questionnaire were used to collect data. The results show that the authentic leadership and its components —including self-awareness, an internalized moral perspective, relational transparency, and balanced processing—have been practiced by the principals and teachers in Islamic Secondary Schools. Authentic leadership applied in MA is better than those in MTs. The authentic leadership has been internalized in the teaching of Prophet Muhammad in terms of sidiq (truthful), tabligh (advocacy), amanah (trustworthy), and fatonah (wisdom) as the core values in the daily school community practices. Teacher performance evidently improves with involvement in decision-making, communication processes, and the delegation of authority. Differences appear in practice, that MTs principals demonstrate less competency than senior counterparts because of their relative educational backgrounds and experiences. This study is limited in that it used non-probability sampling implying that the results cannot generate any context. This study originates in Islamic schools in Indonesian context that school reform is now in the process of change.