This study draws on the activity theory to explore how bilingual first-year secondary school students appropriate resources strategically in response to linguistic challenges in learning science through English in Hong Kong. The study explored 12 bilingual students' self-regulated strategy use by conducting in-depth interviews, stimulated recalls, observation and analysis of learning materials. Through analyzing these data, we examined how and why they appropriated and used resources strategically for self-regulated learning. The analysis revealed that the participants had used various artefacts (e.g. dictionary) and rules (e.g. evaluation criteria) to negotiate their respective roles (e.g. subject content learners and language learners) in situated communities of learning that consist of subject teachers, classmates, family members, private tutors and friends. Similarities and differences were found between the high achievers and the underachievers with regard to the use of resource-mediated strategies and the underlying reasons. The results inform the development of pedagogical schemes to enhance bilingual students' self-regulated strategic learning of academic subjects through English. Copyright ©Routledge.