This study elucidates the relationship between instructional leadership and teacher self-efficacy by identifying the moderating role of teacher collegiality. Survey data were collected from 1,498 teachers at 53 middle schools in Henan, China. Findings indicate that instructional leadership has a positive impact on teacher self-efficacy. More importantly, teacher collegiality was found to moderate the relationship between principal instructional leadership and teacher self-efficacy. More specifically, when there was a high level of teacher collegiality, instructional leadership positively predicted teacher self-efficacy; however, when there was a low level of teacher collegiality, instructional leadership barely predicted teacher self-efficacy. In addition to elaborating on the relationship between principal instructional leadership and teacher self-efficacy, this study underscores the importance of teacher collegiality in promoting the effectiveness of instructional leadership.