In this article we argue that Second language learners need Metaphorical Competence (MC) which is the ability to comprehend and use metaphors in natural communication. The lack of knowledge of metaphorical concepts often leads learners to get off on a wrong foot. Learning idiomatic expressions helps learners for better communication as well as language learning in the target culture and society. This paper reports on a study done to inspect the development of conceptual fluency and metaphorical competence in Persian students of English. A group of intermediate language students were selected to be examined for the usefulness of idiomatic expressions' instruction. At the end of the instruction it was revealed that it is possible to improve learners' conceptual fluency (CF) by the extended exposure to idiomatic expressions