Öz The objective of this study was to investigate the understanding of  transparent and opaque English idiomatic  expressions of  Turkish students. In order to carry out the study, randomly selected 35 intermediate and 36 advanced level students  in the Department of English Language and Literature at Kafkas University, Kars, Turkey, were given a 40-item containing Turkish version of idiomatic expressions and a 40-item containing English version of different idiomatic expressions. The students were wanted to write the equivalences in English and Turkish. According to the result of the study, Turkish students can understand transparent and common opaque idioms more easily.  However, if the idioms are both opaque and uncommon, they cannot get their meanings if they haven’t learned them directly. The result of the study has indicated that  there is no significant difference between intermediate and advanced students in understanding transparent, opaque/common and opaque/uncommon idioms, however, a significant difference  has been observed between the subjects to transparent, opaque/common and opaque/uncommon idioms in both for the answers from Turkish to English and English to Turkish (p<0,001). The highest scores are those for the transparent idioms which are followed by opaque/common and opaque/uncommon, respectively.