This study aimed at exploring the effect of implementing writing metacognitive strategies via flipped classrooms on the Iranian EFL learners' achievement, anxiety, and self-efficacy in writing. The study involved 45 intermediate learners of both genders, selected using a random convenience sampling method. The participants' English proficiency was measured by the Preliminary English Test, and they were placed in two groups: experimental group (23 learners) and control group (22 learners). In the former group, the students were exposed to 5 distinct types of metacognitive strategies over the course of 10 flipped classroom sessions, while the latter group received writing metacognitive strategy-based instruction in a traditional classroom setting. The data collection process involved administering the Second Language Writing Self-Efficacy Scale, two intermediate writing tasks, and the Second Language Writing Anxiety Scale. The collected data were analyzed using a one-way ANCOVA. The findings evidenced considerable enhancement in the writing performance of the students who underwent instruction through flipped classrooms in comparison to those in the traditional classroom refsetting. Furthermore, the results demonstrated that the utilization of writing metacognitive strategies in flipped classrooms resulted in a substantial rise in students' writing self-efficacy, while simultaneously leading to a decrease in their writing anxiety.