AbstractThe use of mother tongue in foreign language classes has been a controversial issue in the history of language teaching. The purpose of this study is to examine the effectiveness of using L1 in teaching vocabulary to EFL students. To do so, 72 participants (36 boys and 36 girls) were divided into 6 classes in three levels based on their language proficiency, namely beginner, elementary and preintermediate. The students in each level were randomly assigned to control and experimental groups. In order to measure the effect of using L1 on their vocabulary learning, the control and experimental groups were taught for 20 sessions through the use of different methods. In the experimental groups, after teaching the new words through images and pictures, students’ L1 was used to tell the students the Persian meaning(s) of the words, while in the control group, the Persian meanings were not told to the students and only the target language and visuals were used for teaching the new words. The.....