<p>Lexical inferencing as an efficient strategy to deal with unfamiliar words is suggested to be the most commonly used strategy among students, thus it has attracted much attention in the comprehension literature. While literature abounds with inferencing studies in reading, few studies have delved into the processes involved in listening. This study sought to investigate the role of depth of vocabulary knowledge (DVK) in lexical inferencing success and determine the relationship between students' DVK and listening proficiency. To this end, 56 upper-intermediate TOEFL applicants from 2 language institutes in Iran participated in this study. The participants were assigned to three levels of High- Mid- and Low-proficiency and in a consequent session were required to take the 40-item DVKT (Depth of Vocabulary Knowledge Test). In the final step the students sat for the lexical inferencing task and were required to identify the meaning of 17 unfamiliar words in 8 listening excerpts. The results indicated that DVK was a determining factor in lexical inferencing success, and that there was a positive relationship between students' DVK and their listening proficiency.</p>