Abstarct: Abstract One of the most crucial problems English language learners encounter in learning English is speaking problems. Learners are grammatically competent but communicatively incompetent. Therefore, the present study aims at exploring the effect of discourse-baxsed grammar instruction approach on Iranian EFL learners` speaking ability. In order to achieve the objective of the study, 60 students who were studying English at a language institute in Mashhad were selected and randomly assigned to the control and experimental group. The experimental group was treated with discourse-baxsed grammar instruction while the control group just received the traditional method of grammar teaching through 8 instructional sessions, including 2 sessions per week. Both groups were pre and post-tested. To this end, an IELTS speaking test was selected. The collected data from the study was analyzed through paired and independent sample T-test. Results of the study revealed that there was a significant difference at p < .05 in the performance of the two groups on speaking. The results of the study can have significant implications for researchers, teachers, material developers and teacher trainers in their academic journey. Teachers can take advantage of this method in their classes as an effective approach of teaching. Results can be also useful for material developers and teacher trainers in designing course books and pre-service programs. Findings may pave the way for other researchers to do more similar studies.