This study aims to identify the level of transformational leadership of principals and the level of school effectiveness in TS25 schools in Gua Musang District, Kelantan. In addition, this study also seeks to look at the relationship between the two variables involved, transformational leadership and school effectiveness. This quantitative study by cross-sectional survey method used two types of instruments, namely the Transformational leadership instrument by Leithwood and Jantzi (1999) and the school effectiveness instrument adapted from the study of Lazaridou and Iordanidis (2011. The sampling of the study involved four TS25 secondary schools with a total of 162 teachers. The findings of the study showed that the level of transformational leadership of principals and the level of school effectiveness was at a high level, with values (M = 4.17, SP = .604) and (M = 4.19, SP = .613) respectively. Further, correlation analysis showed that there was a very strong and significant relationship (r = .89, p <.01) between the two variables involved, namely transformational leadership and school effectiveness. It is hoped that the findings of this study can be used as a guide by the parties involved, especially the Ministry of Education Malaysia in strengthening the characteristics of high-performing leadership among school administrators towards improving school effectiveness through professionalism programs.