The widespread of mobile devices bring a huge potential to e-leaning in terms of pervasiveness, ubiquity, personalization, and flexibility. In this study, a total of 70 university ESP learners were involved. Telegram, as the treatment in this study was compared to a conventional method; face-to-face in the cooperative writing activities. First of all a pre-test was administered to all students and based on the preliminary results; students were divided into Telegram and face-to-face Cooperative writing groups. After using both approaches, a post-test was given to participants. Then, a questionnaire was given to the students in order to investigate the effect of Telegram on the attitudes of ESP vocabularies and expressions by the ESP learners. The data were then analysed using independent t-test and paired sample t-test. From the findings, it was found that participants in Telegram Cooperative writing groups displayed slightly higher scores compared to face-to-face Cooperative writing groups. However, the differences between Telegram and face-to-face Cooperative writing groups were not significant in the post-test writing scores. When comparison was made within each group, this study found that there were significant differences for overall writing performance, content, organization, vocabulary, language use and mechanics. The results also indicated that the students had positive attitudes toward using telegram Cooperative learning.