Vietnam has been making its way into the global economy, and on that account, the learning of English has been of paramount importance, especially English for Specific Purposes. However, it remains controversial whether mother tongue should be used in ESP teaching due to existence of debatable theories on the presence of L1 in L2 classrooms. This study investigated the practice of using Vietnamese by teachers at University of Languages and International Studies, as well as the perceptions of ESP students towards employing Vietnamese in ESP classrooms. Data was collected by means of questionnaires and semistructured interviews with 65 EnglishInternational Economics undergraduates. The findings revealed that ESP practitioners often used Vietnamese in specific situations such as explaining technical terms, establishing rapport with students and addressing administrative issues. The results also suggested that ESP learners regarded mother tongue as a doublededged tool in ESP classrooms. In addition, recommendations in terms of pedagogical methodology and improvements were also proposed for further related studies. Vietnam has been making its way into the global economy, and on that account, the learning of English has been of paramount importance, especially English for Specific Purposes. However, it remains controversial whether mother tongue should be used in ESP teaching due to existence of debatable theories on the presence of L1 in L2 classrooms. This study investigated the practice of using Vietnamese by teachers at University of Languages and International Studies, as well as the perceptions of ESP students towards employing Vietnamese in ESP classrooms. Data was collected by means of questionnaires and semistructured interviews with 65 EnglishInternational Economics undergraduates. The findings revealed that ESP practitioners often used Vietnamese in specific situations such as explaining technical terms, establishing rapport with students and addressing administrative issues. The results also suggested that ESP learners regarded mother tongue as a doublededged tool in ESP classrooms. In addition, recommendations in terms of pedagogical methodology and improvements were also proposed for further related studies.