The purpose of this study is to understand the current status of preschool teachers’awareness of the instructional leadership of principals (directors), teachers’ professional learning communities and their teaching effectiveness, and to explore the relationship between them. The research methods were literature review and questionnaire survey, and the research subjects were pre-school educators of Taiwan’s public preschool. A total of 996 questionnaires were sent out, among which 630 samples were valid with a recovery rate of 84%. After recovered, the questionnaires were analyzed with statistical methods such as confirmatory factor analysis, descriptive statistics, product moment correlation and structural equation modeling. The results showed that preschool teachers’ awareness of the instructional leadership of the principal (director), teachers’ professional learning communities, and teaching effectiveness are good, and are correlated. The positive influence model has good fit. It is found that the teacher’s professional learning communities play a full intermediary role between the instructional leadership of the principal (director) and their teaching effectiveness, which means that the instructional leadership of principals (directors)needs to affect teachers’ teaching effectiveness through teachers’ professional learning communities. This study suggests that preschool principals (directors) make good use of the intermediary role of teachers’ professional learning communities and use the instructional leadership to enhance teachers’ teaching effectiveness.