This study examined the relationship between school leaders' instructional leadership and teachers' functional competency in high prestige schools in the Northern part of Peninsular Malaysia. The research design employed for this study was descriptive method of the correlational survey type. This survey was administered to 225 teachers from 12 secondary and primary schools to collect the necessary data. Principal Instructional Management Rating Scale Questionnaire was adopted from Hallinger and Murphy (1985) and Integrated Assessment Module for Education Services Officers (2014) was used to obtain the data. The study found that the level of instructional leadership among the leaders as high (M = 3.94, SD = 0.55) and the level of teachers' functional competency as very high (M = 4.23, SD = 0.41). The finding also revealed that there is a very strong significant relationship between school leaders' instructional leadership and teachers' functional competency (r = 0.956, p = 0.000). The findings further suggested that there is an averagely strong significant relationship (r = 0.397, p = 0.000) between school leaders' instructional leadership and teachers' knowledge; and a positive with weak but significant relationship (r = 0.345, p = 0.000) between school leaders' instructional leadership and teachers' skills. This study recommends that school leaders adopt instructional leadership in their practices to improve teachers' functional competency.