Self-efficacy and positive attitude are among factors contributing to success in language learning, yet encouraging these important traits among language learners in the classroom is often difficult. This study aims to investigate the extent to which a collaborative authentic task helped promote communicative self-efficacy and a positive attitude towards English language study among second-year dental students taking an English for Specific Purposes (ESP) course in a public university in Thailand. Specifically, the students were asked to interview foreigners in English about a topic in the field of dentistry, and then report their findings and reflect on their individual performance and experience during a feedback session with their instructor. Pre-task and post-task questionnaires were developed and distributed to 96 dental students, and a semi-structured interview was used to explore students' attitudes in greater depth. It was discovered that most of the participants perceived that their self-efficacy was higher in some aspects after they had completed the task. Results from the semistructured interviews also demonstrated that this group of students recognized the importance of English in their profession. Furthermore, the overall attitude of the students toward the collaborative authentic task was favorable, with most participants reporting that they found it very useful and challenging as it provided them with the opportunity to use English in real life. Considering the conclusions of the study, teachers are encouraged to implement collaborative authentic tasks in the classroom to enhance students' self-efficacy and positive attitude toward English learning.