This study aimed to identify the relationship of vocabulary size of students to their English language performance. The respondents of this study were taken from B1 Plus students of the English Language and Preparatory Year Institute, Jubail Industrial College- Royal Commission for Jubail. The study used the descriptive correlation research design to establish the relationship of the students’ vocabulary size to their performance in English. Pearson's correlation coefficient (r) was used to measure the strength of relationship between the two variables- vocabulary size and English performance. Vocabulary Level Test, adapted from Nation (1990) , was used to measure vocabulary size, and the final mark result in B1 Plus was used for the English performance of students. Based on the findings, vocabulary size has no significant relationship to listening and speaking skills of students. However, vocabulary size has a significant relationship to reading and writing, grammar, e-learning, and overall English language performance of respondents.

vocabulary size, English language performance