Collocation is an aspect of language usually defined as two or more words which co-occur and must be learned as an integral whole (Palmer, 1933). L2 learners should have a rich collocational competence to communicate effectively and fluently. Despite the importance of collocations in second language learning and teaching, few studies have yet been carried out to investigate the collocation knowledge of Iranian English for Specific Purposes (ESP) postgraduate students. Therefore, this study aimed at studying the relationship between general English proficiency and collocation knowledge of these students. This study also explored the impact of type of test (receptive vs. productive) on the students’ performance in collocation tests. Finally, the collocation knowledge of the students was investigated across different fields of study and different collocation categories. For the purposes of this study, 100 ESP master’s students majoring in different fields of study were selected randomly from three national universities located in Yasuj and Kashan provinces. The participants took a collocation test including a receptive multiple-choice test and a cued productive translation test. Before the collocation test a general English proficiency test was administered to measure the general English proficiency of the participants. Both grammatical and lexical collocations were examined in the study. The results were analyzed through both descriptive and inferential statistics. The results showed that there was a high positive correlation between general English proficiency and collocation knowledge of the students. The results also indicated that the participants had more difficulty with the productive test rather than the receptive test. Furthermore, the overall collocation knowledge of the students was significantly different across different fields of study and various collocation categories. It could be concluded that increasing knowledge of accurate collocational patterns, especially the productive collocation knowledge, is necessary for Iranian ESP postgraduate students.
Key words: Collocation, Collocation knowledge, English for Specific Purposes, Postgraduate students