This study examines the frequency and pattern of interpersonal interactions between the learners and instructors of an online English language learning course offered at a Vietnamese university. The paper begins with a review of literature on interaction type, pattern and model of interaction followed by a brief description of the online environment and its learners and instructors. The online messages extracted from the communication forums were analysed using simple descriptive statistics and content analysis techniques in the light of Salmon's (2003) model of online teaching and learning to explore the frequency and pattern of interaction. The results of the study indicate that after a high level of engagement at the beginning of the course, the learners' interaction dropped and different patterns interaction were found in the three communication forums of the online course.