This study investigated the role of Telegram, a mobile messenger app, in mastering receptive and productive knowledge of vocabulary by Iranian EFL learners. In addition, it was intended to survey EFL learners’ attitude toward using telegram to learn English vocabulary. Therefore, both quantitative and qualitative design were used. So, 57 students were selected from a language institute in Isfahan, Iran. To homogenize the participants, Oxford Quick Placement Test (OQPT) was administered and the participants were divided into two groups accordingly, a Telegram group and a control group. At the beginning of the study a checklist of words was given to the participants. Afterward, during the study, the experimental group received the treatment (teaching words via telegram), while the control group received the target words traditionally. After 8 sessions, 20-30 minutes each, an achievement test was administered to the groups. The results of Independent Sample t-test revealed a statistically significant difference between the achievement test scores of the experimental and control group. Moreover, the participants had positive attitude about using Telegram to learn English vocabulary. The findings of this study may inspire teachers to use mobile applications and also course developers to modify and improve not only the curriculum, but also the methodology of teaching vocabulary.
