This study was an attempt to investigate the particular role of learners’ depth and breadth of vocabulary knowledge in their listening comprehension. Moreover, it also sought to find out whether there is any difference between high and low listening proficiency groups in performance on depth and breadth dimensions of vocabulary knowledge. To this end, a total of 117 junior university students majoring in English language and literature participated in the study. In order to assess the learners’ listening comprehension, the listening section of a paper-based version of the TOEFL was administered. Their depth and breadth of vocabulary knowledge were measured through performance on Word Associate Test and Vocabulary Levels Test, respectively. The results of data analysis indicated that both depth and breadth of vocabulary knowledge are determining factors in successful listening comprehension. However, it was found out that breadth or size of vocabulary knowledge provides a more significant contribution than depth to listening comprehension. Furthermore, the results of the study indicated that depth and breadth of vocabulary knowledge are not significant predictors of listening comprehension in the low listening ability group.