The effect of Locus of Control (LOC) on L2 learners'' achievement has scarcely been examined within the context of Iran. This study is concerned with examining the relationship between EFL learners'' LOC and their L2 reading and L2 writing achievement. It also explores the relationship of LOC with use of language learning strategies among EFL learners. To do so, the researcher first validated the Persian version of Internal Control Index (Duttweiler, 1984) to measure the particpants'' LOC. The Persian version of Strategy Inventory for Language Learning (Tahmasebi, 1999) was also used to measure the participants'' language learning strategies. The results of the study indicated that 1. There is a significantly positive relationship between EFL learners'' LOC and both their L2 reading and L2 writing achievements. 2. There is a significant and positive relationship between LOC and use of language learning strategies. 3. The interaction of LOC and gender has no significant effect on use of language learning strategies. The results of the interviews clearly corroborated those of the questionnaires.