Idioms have long been regarded as problematic for L2 learners due to the arbitrariness of their meanings and forms. Traditional methods of teaching idioms focus on rote learning and memorization. Recent developments in cognitive linguistics research have considered idioms as analyzable expressions which are motivated by conceptual metaphors and whose meanings can derive from associations between source and target concepts. Believed to be imageable and comprehensive, idioms should be learned through the process of raising L2 learners’ awareness of conceptual metaphors behind these expressions. Nevertheless, these methods fail to notice culture entailments embedded in conceptual metaphors. Especially for FL learners who share neither common cultural background nor living environment with the target language users, difficulties resulting from transferability between L1 and L2 idioms owing to cultural similarities and differences may be serious. To bridge the gap between idioms and conceptual metaphors caused by cross-cultural differences, this study suggests a teaching method by incorporating the idea of metaphoric mappings. A case study was conducted in an EFL writing class to investigate the effect of the methods. Essays written by the students before and after the instruction were analyzed. Results showed that the students increased frequencies of using not only common idiomatic expressions but also creative analogies comprising vivid images based on the conceptual metaphors taught. Additionally, they used L2 expressions whose conceptual metaphors also existed in L1 more often then expressions whose conceptual metaphors were exclusive in L2. Such findings affirm the importance of culture and provide valuable insight to EFL teachers in adopting cognitive-oriented method to teach English idioms.