The focus of the present study was to explore the effect of self-directed learning method on Iranian EFL students’ writing achievement in two levels of language proficiency (pre-intermediate and intermediate). It also attempted to find out if there was any significant difference between two groups of learners, control and experimental, in each level regarding their development of writing skill. In order to reach this goal, 30 male EFL learners that were selected based on random sampling, participated in this study. After the treatment was over, both groups in each level were given the post-test, the results of which were compared with pre-test results. Then, an independent sample t -test was run to find the effectiveness of two approaches to detect the differences among the means of the two groups in each level. The results of the present research indicated that the self-directed learning method had significant effects on the pre-intermediate and intermediate students’ performance of English writing ability. The results also indicated that there was a significant difference between the two groups of learners in each level regarding their development of English writing ability.
