The present study mainly investigated the effects of vocabulary knowledge and dictionary use on EFL reading performance. The results show that scores on vocabulary size, specific vocabulary knowledge, and reading comprehension are highly and positively correlated. Scores on specific vocabulary knowledge are more closely correlated with reading comprehension than scores on vocabulary size. Scores on specific vocabulary knowledge adds a noticeable prediction in reading comprehension over and above the prediction already afforded by scores on vocabulary size. The additional prediction can be explained by the ability to infer from the context, activating content schemata and the knowledge of polysemy of the words. It is also found that learners often overestimate their understanding of words. The results also show that the access to a bilingual electronic dictionary has a significant effect on the reading scores for both high proficiency group and low proficiency group. It is due to quick access to electronic dictionaries and relatively limited control of vocabulary in English.