The article offers an in-depth lexical analysis of the listening sub-test of the famous International English Language Testing System (IELTS). The vocabulary profile of 239 listening transcripts from 60 IELTS official practice tests were analyzed. The results showed that, 3,000 most frequent word families in the British National Corpus/Corpus of Contemporary American English (BNC/COCA) word list were necessary to safely gain 95% coverage of all four sections in the test. Meanwhile, a vocabulary knowledge at the 5,000 level would secure the 98% coverage. The study also reveals that, with the support of 570 word families from the Academic Word List (AWL), learners only need to be familiar with 2,000 word families to achieve 95% coverage of the first, second, and third listening sections, equaling 75% of the IELTS listening test. The differences in lexical demands between listening sections were also highlighted.