The purpose of this quasi-experimental study was to investigate the effect of metacognitive writing strategy instruction on Iranian EFL learners’ writing performance, anxiety, and self-efficacy. To accomplish the objectives of the present study, a sample of 30 Iranian EFL students was recruited. The recruited participants were the students of the intermediate level at Safir Institute in Songhor, Iran. The participants of the study were students of two intact classes which were randomly assigned to the control group (n=15) and experimental group (n=15). The intact groups were given different instructions that the pupils in the experimental group were instructed in improving writing skills through the metacognitive strategy and the pupils in the control group were instructed in traditional writing skills. All pupils were asked to write a composition according to given topics in the pre- and post-tests. The Writing Post-test Essays were scored to see if there was a significant difference in those essays prepared by learners who had explicit instruction in metacognitive strategy use as compared to those who did not receive the instruction. The quantitative data were collected by the SLWAI ,SLWSS and Timed writing essays as pre-test and post-test in both groups, that descriptive statistics, Independent-Samples t-test, One-Way ANCOVA, and Multivariate Analysis of Variances were conducted to analyze them and the qualitative data were collected by the interview, and to analyze the qualitative data the transcripts were thematically coded using the principles of content analysis proposed by Auerbach and Silverstein (2003). Finally, The results indicated that metacognitive writing strategy instruction significantly improve Iranian EFL learners' writing performance, reduces the writing anxiety, and enhances their self-efficacy.
