Teachers' pedagogical beliefs (PB) and knowledge base of teaching play a prominent role in determining their instructional practices, including instructional material use (MU). Instructional materials provide students with information and facilitate learning, allowing meaningful learning. However, teachers' MU likely affects the effectiveness of their teaching, and the decision on their MU relies on their PB and their knowledge base of teaching, which includes pedagogical knowledge (PK), content knowledge (CK), and pedagogical content knowledge (PCK). Although some studies have investigated how teachers' PCK affects their pedagogical beliefs, studies, which investigate the interrelationship between teachers' PB, PCK, and MU, are absent. Consequently, there is yet an instrument that measures the interplay of these essential factors in English language teaching (ELT). Therefore, this study aimed to adapt and validate the EFL teachers' PB, PCK, and MU. Two hundred sixty in-service secondary school English teachers in Indonesia participated in the study. The validated version of EFL teachers' PB, PCK, and MU (EFLT-PBPCKMU) had six factors and 25 items measuring teachers' PB, PCK, and MU using the 5-point Likert scale. The EFLT-BPCKMU scale had satisfactory psychometric characteristics and model fits, as demonstrated by exploratory and confirmatory factor analysis results.