Writing in a second or foreign language seems to be the most difficult language skill for language learners to acquire in academic contexts. While explicit instruction of strategies is not a usual practice in foreign language classrooms, it could be beneficial for language learners. The present study aims at investigating the effect of concept mapping strategy on EFL learners' writing performance. To this end, sixty Iranian students at the intermediate level of language proficiency participated in the study. Their language proficiency was determined by Michigan Test of English Language Proficiency. The results of the Analysis of Covariance revealed that the instruction of concept mapping strategy had a positive effect on EFL learners' writing achievements. The findings have some pedagogical implications for teaching language skills and designing strategy-based syllabus leading to successful language performance. Keywords: Concept mapping, Explicit instruction, Learning strategy, Writing achievement 1. Introduction Writing is a complicated process which involves a number of cognitive and metacognitive activities, for instance; brainstorming, planning, outlining, organizing, drafting, and revising. Cognitive aspects of writing have received a particular attention, as investigators have attempted to understand the thought processes underlying the compositions of students (Flower & Hayes, 1981). According to Omaggio Hadley (1993), writing requires composing, which implies the ability either to tell or retell pieces of information in the form of narratives or description, or to transform information into new texts, as in expository or argumentative writing. Therefore, it is best viewed as a continuum of activities that range from the more mechanical or formal aspects of writing down on the one end to the more complex act of composing on the other end. A substantial body of research suggests that training students to use language learning strategies can help them become better language learners. Early research on "good language learners" (Naiman, Fröhlich, Stern, & Todesco, 1996) suggested a number of learning strategies that successful students employ when they learn a second or a foreign language. A study of O'Malley and Chamot (1990) suggested that effective L2/FL learners are aware of the learning strategies they use and why they use them. Meaningful learning according to Ausubel's (2000) theory occurs when students intentionally attempt to integrate new knowledge with existing knowledge. A learner who attempts to integrate knowledge has a more extensive network of knowledge and therefore more retrieval paths. Richards, Platt, and Platt (1992) presented a specific definition of strategy training and outlined three different approaches: "[It is] training in the use of learning strategies in order to improve a learner's effectiveness. A number of approaches to strategy training are used including: 1) Explicit or direct training: learners are given information about the value and purpose of particular strate...