As societies globalize, mastery of a second language or multiple languages has become an important index to enhance interaction in the society, in that English is a widely used medium of communication globally. For engagement in international business, commerce, science, technology, and governance, the benefits of an efficacious English language teaching force to facilitate the English acquisition process of students in classrooms around the world is highly valued. The objective of the research was to investigate the possible factors (internal and organizational) related to EFL teacher's self-efficacy in Macao (Chinese Medium Instruction context) via qualitative approach. As evidenced through the EFL teachers' interviews, teachers' experience, as well as some external factors in term of working environment, organizational socialization, and work engagement can be possible factors positively related to their self-efficacy. Recommendations for the school management and educational department to enhance and sustain the efficacy of EFL teachers were discussed.