The building of professional learning communities has been widely recognized as an effective strategy for schools wanting to improve student performance and enhance teachers' professional capacity. This study explored the relationship between leadership practices and professional learning communities, with a particular focus on the mediating role of trust in colleagues within the context of mainland China. A total of 215 primary school teachers in a province of southwestern China participated in the study. The results showed that leadership practices and trust in colleagues had positive effects on five factors of professional learning communities, namely a shared sense of purpose, collaborative activity, collective focus on student learning, deprivatized practice, and reflective dialog. Trust in colleagues also mediated the influence of leadership practices on professional learning communities. The implications for facilitating professional learning communities in mainland China are discussed here.