Using first language in EFL classrooms has been a matter of controversy over the years. Language learners make use of their mother tongue consciously or unconsciously when learning a language. In Iranian EFL classrooms, teachers sometimes use first language to make learning more dynamic and to give their students a feeling of security. Several factors influence the use of first language in EFL classrooms. This study aimed at examining those factors along with teachers' perceptions toward the use of first language in teaching. To this end, the researchers followed a mixed-methods approach using open-ended and closedended questions, interviews, classroom observations, and focus group discussion. The results showed that, students found using L1 in the classroom useful. They believed that it is time-saving, effective, anxietyreducing, and motivating. Moreover, the use of L1 can scaffold the students who cannot accomplish the tasks on their own. Some students, however, had opposing views toward using L1 in the classrooms.