High-stakes tests exert impacts on teachers’ perceptions, methodology, practices, and materials used in the classroom. However, previous research studies have overlooked the role of teachers’ past experiences in the tests and their instructional planning prior to, during, and after the preparation courses. This study inspected the washback effect of IELTS examination on Iranian EFL teachers’ instructional planning considering their IELTS related experiences. Through a mixed-methods research design, two sets of questionnaires were distributed among 120 Iranian IELTS instructors to examine the IELTS washback effect on their perceptions of instructional planning. Afterward, a semi-structured interview was held with 15 instructors, selected from among 120 initial participants, to supplement the previously collected data. The results of one sample t-test and Wilcoxon signed-ranks test indicated that the current level of Instructional planning at item and total score level was beyond average. Likewise, the results of Spearman rho indicated a positive and significant relationship between instructors’ instructional planning and their past IELTS related experiences. It was also found that the IELTS examination made the instructors develop exam-oriented plans by focusing on the students’ test performance. The results are invaluable for IELTS instructors in that they can raise their knowledge and awareness about the nature and scope of IELTS washback effect and ways to develop exam-oriented plans.
