The relationship between the leadership competence and instructional leadership of school principals is an issue in education towards improving the effectiveness and efficiency of the management of a school. This study aims to explore leadership competencies and instructional leadership practices and their implementation by island school principals in the state of Sabah. This qualitative study applies a case study approach. A total of 12 participants consisting of principals, senior curriculum assistants and subject teachers were involved in this study. The data collection process was done using the methods of interviews, observations and document analysis. The data were processed and analyzed using ATLAS.ti 8. The data findings are guided by the theory of leadership competencies and instructional leadership. Leadership competencies theory emphasises the domain of behaviors, knowledge and skills. While instructional leadership involves three main domains namely defining the mission of the school, managing instructional programs and creating a positive school climate. The findings of the study indicated that leadership competencies and instructional leadership are essential for school principals on the island to ensure the school quality can be achieved.