Cognitive styles influence the performance of language learners and can predict their success in the process of language learning. Considering field dependence/independence cognitive styles, this study aims at determining if they are significant in English vocabulary knowledge. A number of EFL university students took part in the study. The investigation was done through using Vocabulary Size Test (VST) (Nation, 2007) and the Group Embedded Figures Test (GEFT) (Witkin, Oltman, Raskin, and Karp, 1971). Using the Vocabulary Size Test (VST), the participants were divided into three groups of high, mid, and low. Moreover, with respect to the Group Embedded Figures Test (GEFT), they were divided into two groups, field dependents and field independents. Mean score comparison revealed there was a credible and meaningful relationship between field dependence/independence cognitive styles and total vocabulary knowledge. It was also indicated there was a significant relationship between field dependence/independence cognitive styles and vocabulary knowledge in the high and mid groups. Finally, based on the findings, teachers should take learners’ individual differences into consideration so that they could adopt and apply teaching methods in line with the learners’ various cognitive styles.