As idioms are found in daily language in various types of discourse including conversations, lectures, newspaper and magazine articles, movies, radio broadcasts, and television programs, lack of idiomatic knowledge may lead to miscomprehension and even communication breakdown. Furthermore, idioms and metaphorical expressions are considered crucial in developing fluency. As such, language learners need to develop their competence in idiomatic expressions. Of special place are the idioms formed based on conceptual metaphors as they are rooted in cultural norms and show the conceptual understanding of language speakers. L2 teachers should raise their learners’ awareness of such idioms to help them develop their language competency. The objective of the present study is twofold: (1) to investigate the effect of metaphorical awareness on learning metaphor-based idioms of the Persian language by Persian learners, and (2) to investigate different modes of this effect. Through qualitative and quantitative analyses of ten Persian language learners’ performances, before and after receiving metaphorical awareness, it was found that metaphorical awareness in 71.29% of cases had a positive effect on the participants’ learning of metaphorical idioms, in 6.5% of cases had a negative effect, and was of no effect in only 9.78%. Also, in 12.39% of cases, it was not possible to clearly specify the effect (or lack thereof) of metaphorical awareness. Implications for enhancing metaphorical awareness in language learning classes are further discussed.