Second language learners have difficulty in vocabulary learning since many English words have two or more meanings especially when they occur in idioms or expressions and deciding the correct meaning is demanding for EFL learners. So, this study aimed at investiating how 54 Persian students of English at intermediate and advanced levels which included 28 advanced students and 26 intermediate students, used their first language knowledge to comprehend and produce 3 types of English idioms, namely compositional, semi-compositional, and non-compositional ones. Compositional idioms, which are totally word for word translation of English idioms in learners mother tongue, like: Be on the tip of one’s tongue. Semi-compositional idioms which are syntactically or semantically similar but differ in one or more words, such as: for a rainy day. Non-compositional idioms which are totally different in translation from learners mother tongue, for example, drive someone up the heel. The students were divided into 4 groups; 2 experimentals and 2 controls. A pretest which included both comprehension and production tests was administered to each group. Then, the experimental groups received the treatment in the form of small conversations, but the control groups did not receive any treatment. In the last session all groups received an immediate posttest. After one month, a delayed posttest was adminstered. For the analysis of the data, a t-test and ANOVA were employed. Results in the four groups showed that compositional idioms had the highest correct responses, followed by semi-compositional idioms, and non-compositional idioms were the most difficult to comprehend and produce. In addition, in all groups students performed better in comprehension rather than production test.