Abstarct: Abstract The most important purpose of learning a foreign language is to be able to communicate in that language. As a result, students’ willingness to communicate has been the focus of study for decades. In this regard, the effect and relation of different influencing factors on students’ willingness to communicate has received the attention of research. However, no study so far sought to establish the effect of mother tongue use on students’ willingness to communicate. Therefore, this study aimed to investigate the effect of mother tongue use on EFL learners’ willingness to communicate. To this purpose a true -experimental research was done by the researcher. To this end, 68 students, 49 females and 19 males, aged between 18 to 26, who were EFL learners studying English language at elementary level in two institutes in Tehran were randomly selected and then randomly assigned to control and experimental groups. A pre-test and post-test using MacIntyre et al. (2001) questionnaire was administered to measure learners’ willingness to communicate. The number of sessions, course book (Top Notch 1), materials, audio-visual aids (AVAs), and activities, were precisely the same for both groups. However, in the experimental group, the researcher used L1 to give instructions, teach abstract words, and to explain grammatical rules. After collecting the data and analyzing them, we found a significant difference between the post-test and pre-test values in the experimental group. Analysis also revealed a significant difference between the post-test values of the experimental group and the control group. In short, the findings clearly show that using mother tongue has a significant positive effect on learners’ willingness to communicate.