This study aims to examine the factors influencing pre-service Physical Education (PE) teachers' perception of a specific constructivist approach--Teaching Games for Understanding (TGfU) in Hong Kong. By adopting a qualitative approach, 20 pre-service PE teachers were recruited for individual semi-structured interviews. Deductive data analysis was utilised to identify unique themes with broad aspects of influencing factors. Using Piaget's cognitive constructivism and Vygotsky's social constructivism as the theoretical frameworks, individual factors such as game knowledge, teacher beliefs, learning and teaching experience and social factors including government policy, teacher support and professional culture were identified as key influences in pre-service teachers' perception of TGfU. Furthermore, individual and social factors interplay with each other. In conclusion, cognitive and social constructivism was identified as a useful theoretical framework for illustrating and analysing the factors influencing pre-service teachers' perception of TGfU. (Contains 1 figure.)