This study explored the characteristics of professional learning communities (PLCs) in Hong Kong primary schools. It investigated the profiles of the strengths of professional learning community in schools under study and particularly examined the practices in schools which were identified as strong PLCs. It extends research on PLCs in the Hong Kong context and formulates a quantitative perspective to compare and validate PLC variables across schools in Hong Kong. The Professional Learning Community Questionnaire (PLCQ) for Hong Kong schools was developed to assess the PLC practices in six different areas: leadership for teacher learning, collaborative learning capacity, student-focused orientation, a culture of sharing, mutual understanding and support, and continuous professional development. A composite construct, the Professional Learning Community Index (PLCI) expressed in quantitative terms was utilized to assess the strength of PLC in a school. The research findings show that within the schools which were identified as strong professional learning communities, both the school leaders and teachers had strong emphases on the six subscales of the PLC practices.