This study examined the relationship between school principals' readiness for self-directed learning and their perception of job performance. The study covers public and private secondary school principals affiliated with the Ministry of National Education serving in Istanbul in the 2021-2022 academic year. The data obtained from 316 randomly selected principals were expanded with data collected from 406 principals. The data were transferred to the SPSS 28™ program, missing and incorrect data were checked, 22 data were eliminated with extreme value analysis, and then normality tests were performed. The analyses show that there is a high level of positive relationship between the level of school principals' self-directed learning readiness and their perceptions of job performance. The level of school principals' self-directed learning readiness and job performance perceptions are generally at a medium level and are positive in terms of sub-dimensions. It was found that female school principals have higher levels of self-directed learning readiness and job performance perceptions than males. It was determined that private school principals received higher scores than public school principals. No significant difference was found according to age and education level, but differences were observed according to age groups in the dimension of desire to learn. In line with the research findings, the recommendations of the study includes organizing education programs to improve school principals' self-directed learning skills, developing digital education materials such as podcast, short videos, blogs, bulletin related to school principals' professional development, organizing conferences and seminars related to issues that principals face in the school systems, using social-media groups to enhance communications and support principals' job performance.