This study aimed at investigating the effectiveness of using graded readers for developing EFL preparatory stage pupils' writing skills in terms of vocabulary, grammar, content, organization and mechanics. The participants of the study were forty six (46) second year preparatory stage pupils from Qallin preparatory school for girls, Kafr el-Sheikh, Egypt. The study adopted the quasi-experimental research design, with one research group. Instruments designed and used in the study were writing skills' inventory, pre post writing test and analytical rubric. The experimental treatment was conducted during the second semester in the academic year 2018/2019. The pre-post writing skills test was administrated.  Findings of the study indicated significant differences between the mean scores of the research group on the pre and post writing test on all five sub-skills in favor of the post test. The results showed that using graded readers enhanced the pupils' EFL writing skills. This study concluded with recommendations pertinent to using graded readers as a tool in teaching writing skills