To investigate the use of language learning strategies (LLS) by Iranian EFL learners across proficiency levels, a total of 180 Iranian adult female EFL learners were selected and divided into three different proficiency level groups. To collect data, Oxford's (1990) Strategy Inventory for Language Learning (SILL) was used. One-way ANOVA procedures were used to analyze the obtained data. The results showed significant differences between the elementary level and the advanced level participants in their use of cognitive strategies, but the differences between the intermediate level group and the other two groups (elementary and advanced) were not significant. The same results were found in the participants' overall use of LLSs. However, in the use of the other five categories of LLSs across proficiency levels, no significant differences were found. The findings also showed that among the six learning strategies of SILL, cognitive strategies were the most frequently used strategy type followed by metacognitive strategies, and affective strategies were found to be the least frequently used type of LLSs.