Abstract Writing is one of the most challenging skill that high school EFL students often find difficult. Regardless of the effort teachers make to bring improvements in the teaching of writing, failures have been observed in students’ writing performance. The study targeted to investigate the effect of using graphic organizers as a prewriting strategy on students’ paragraph writing performance in Injibara Secondary and Preparatory School in the academic year 2018/2019. A group of grade eleven students (N=38) was involved in the experiment based on the use of graphic organizers in the study. To achieve the aims of the study and to find answers to questions of the study, the researcher used one group pretest – posttest or quasi experimental research design. Two tests, a pretest and a posttest, were employed to measure the effect of the intervention, i.e the use of graphic organizers in EFL writing lessons. A semi- structured interview was also conducted to substantiate the result of the tests. A paired sample T-test was employed to see the level of students’ improvement in terms of paragraph writing performance as assessed through grammar, mechanics, organization, and coherence. A statistically significant difference between the pretest and posttest was observed which indicated that the use of graphic organizers helped students to improve their writing performance (p<0.05). Teachers of English Language should expose their students on the regular use of various teaching writing strategies and methods like Graphic Organizers to help them to go for and back in their writing tasks during the writing classes. And as the study proved that Graphic Organizers are effective in teaching writing, further research, however, needs to investigate the effectiveness of other strategies in teaching writing in particular and English Language in general. .