The current study aimed to establish whether linguistic background influences Iranian EFL learners' English proverb and idiom comprehension. The specific research question was whether there is a statistically significant difference between the performances of Persian monolinguals and Persian-Turkish bilinguals in idiom-proverb comprehension on the one hand, and among bilinguals themselves on the other. The performance differences between male and female participants, as well as the age factor were also examined. Subjects included English Language Translation students in University of Zanjan (Iran). Monolinguals were Persian speakers, whereas bilinguals were Persian-Turkish speakers. After administering Nelson English Language Test, English Proverb Test, and Yandell’s English Idiom Test, the results were analyzed through ANOVA, Independent-samples t-test, and Pearson product-moment correlation. Findings indicated that there was no statistically significant difference in the between-group and within-group performances of monolinguals and bilinguals. However, the results showed that males outperformed females in the idiom test, but not in the proverb test. The existence of a relationship between age and idiom-proverb comprehension was not supported. The findings lent support to the arguments proposed by Cummins’s (1976) Threshold Hypothesis – which may thus have some implications for encouraging bilingual education in schools; the findings of this study may also be useful for the curriculum developers and policymakers in multilingual societies.
