It seems that the vocabulary knowledge of Iranian university students for English translation is below minimal comprehension. One possible factor affecting the vocabulary knowledge of students is the oral input presented by professors in their classes. This research seeks to analyze the role of oral input in vocabulary learning. For this reason, twenty- three content courses from B.A. English translation syllabus were selected. Hence, the professors` lectures were recorded and then transcribed. Next the data was analyzed with Range 32, the software developed by Paul Nation. The findings revealed that almost ninety percent of the oral vocabulary items used by professors were in the first 1000 word families that are the most frequent words in English. Moreover, the results showed that the level of vocabulary items used by professors did not change over the past semesters. Therefore, it is clear that one of the possible reasons for students’ inadequate vocabulary knowledge is lack of rich oral input, because students do not have sufficiently strong motivation to work harder to comprehend their instructors. The results of this research bring into focus the need for more systematic preparation and presentation of the vocabulary items in the course syllabus.