Various forms of pre-listening support, such as the provision of vocabulary and topic information, have been used to help second language (L2) learners better understand what they listen to. Results of studies on the effects of vocabulary support have been mixed. Furthermore, there has been little research on the effects of different quantities of vocabulary items and types of word information provided on the listening performance of L2 students of different proficiency levels. Therefore, this study investigated the effectiveness of two different levels of 18-week vocabulary support (an expanded vocabulary-instruction support that targeted both a greater quantity of lexical items and a focus on multiword units vs. an unexpanded vocabulary-instruction support with a focus on single words only) for enhancing listening ability of students of English as a foreign language (EFL) defined as their performance on the listening test of the Test of English for International Communication (TOEIC). The results indicate that the group that received the expanded vocabulary support attained a significant gain and performed significantly better on the posttest than the group that received the unexpanded vocabulary support. The results also reveal that the expanded vocabulary support was particularly helpful for lower proficiency level students. Pedagogical and research implications are also discussed.