This qualitative study framed within socio-cultural theory explored a teacher's oral mediation in her classroom interactions with English as a Foreign Language (EFL) learners. It investigated the teacher's mediation time on the basis of the classification of proactive, reactive, and ongoing mediation, her mediation types were also analyzed based on implicit and explicit mediation. The participants included six female advanced EFL learners and their teacher participated in four videotaped sessions of the classroom interactions. They were interviewed regarding the mediation time and type, and then the teacher was interviewed using stimulated recall protocol. Observation, field-notes, and analysis of the videos were carried out by one of the researchers, too. The results indicated that student hints for receiving help from their teacher in classroom interactions were the best representative of the suitable time for proactive mediation. Furthermore, an increase in the students' hints for receiving more help would change the type of mediation from implicit to explicit. These findings highlighted the importance of teachers' mediations in learners' language development and their contributions to classroom discourse research.