This study attempted to identify communication as a human relational 'path' through which principal leadership influenced teacher professional learning. The data was collected from a sample of 970 teachers from 32 Hong Kong primary schools. Online survey was administered, with two questionnaires to measure teacher perceptions of principal leadership and school capacity. Baron and Kenny' s (1986) four-step causal process for mediation analysis was employed and integrated with bootstrapping method. Further significance of the mediating effects of communication was tested, and the sizes for both the direct and indirect effects in the relationship were made explicit. The findings affirmed the role of communication as a mediator in the relationship between principal leadership and teacher learning.[Copyright © 2016 Rowman & Littlefield.]