This study explores English as a foreign language (EFL) teachers' perceptions of the ecological factors influencing students' use of informal digital learning of English (IDLE). 26 EFL teachers participated in semi-structured interviews and complete a narrative frame. The results of conventional content analysis yielded four categories: macro-system factors (e.g., technological development, educational systems, and English status), micro-system factors (e.g., school and family), chrono-system factors (e.g., current EFL learners’ digital experiences) and personal factors (e.g., age, personality traits, digital literacy, awareness and attitude, and prior experiences with technology). The implications of the findings are discussed for stakeholders in EFL education. •The study explored EFL teachers' views on ecological factors affecting students' IDLE.•The data analysis revealed macro-system, micro-system, and personal factors as key influences.•The findings can inform stakeholders on how to implement IDLE in EFL contexts effectively.