This study examines the vocabulary knowledge of 120 Saudi tertiary students in order to scrutinise their ability to communicate in English. A vocabulary test constructed by Nation and Beglar (2007) was utilised in the study. The findings revealed that the mean vocabulary size of Saudi EFL tertiary students was roughly 3000 words. Nevertheless, most of the participants achieved low scores in the vocabulary low frequency levels. Some participants were unable to answer any item correctly in these low and mid frequency levels. This suggests that while those students might be able to communicate at a basic level, dealing with reading simplified texts and comprehending listening materials, they may struggle with reading authentic texts, producing a high quality of writing and watching English TV programmes and films.