Mostly learners and even teachers of English as a Foreign Language (EFL) are still not able to speak grammatically and fluently just because they lack of the Indonesian language proficiency and comprehension. This research was done to investigate how the Indonesian (Bahasa Indonesia) can assist the teachers and learners of EFL in improving their English proficiency and comprehension. The data were analyzed by applying Miles' and Huberman's framework; data reduction, data display, and drawing then verifying conclusion. The findings showed some positive and negative representative perceptions of the teachers dealing with the roles of the Indonesian in the teaching and learning EFL. The second findings showed and explored the roles of the Indonesian in the teaching and learning EFL. There were five roles by which the Indonesian contribute to such as Functional Equation, Competence Indicator, Linguistic Mediator, Communicative Language Paradigm, and Situational Language Use. The third findings explored the aspects in which the Indonesian had the roles to play in assisting the teaching and learning the EFL such as aspect of the Linguistic Item, aspect of Semantics, and aspect of Pragmatics. There were three other findings in this research that were explored and labeled as Linguistic Competence vs Linguistic Cognition, Cultural Behavior-Based Language, and First Language Interest.