ABSTRACT Educational researchers have been interested in studying teachers’ professional identity to understand this dynamic and multifaceted construct within personal and professional processes through different experiences. In this study, we designed a qualitative case study with Cultural–Historical Activity Theory (CHAT) to examine physics teachers’ professional identity in Turkey. The study aimed to explore the elements of activity systems: teachers’ experiences, community relations, tools, resources, rules, division of labour, and teaching practices. Data sources were interviews, classroom observations and documents, which were analysed by constant comparative method. The results showed that teachers recognised the significance of student-centered instruction, but they often had limitations in terms of resources and exam-based education that led them to adopt traditional instruction. The findings emphasised the need for systemic reforms to balance instructional objectives with teaching realities, supply resources, and make the connection between teacher preparation and classroom enactment. The research results support constructivist epistemology and suggest that the physics education community needs to improve the quality of physics education in Turkey and globally.