Our study examined the language learning strategies of successful and less successful Iranian EFL learners. The sample comprised 1608 junior and senior EFL students who completed the "Strategy Inventory for Language Learning" (SILL), and 30 randomly selected participants in semi-structured interviews. The results from descriptive statistics revealed that: (a) Iranian EFL learners primarily used cognitive strategies while compensation and memory strategies were used the least; (b) successful learners preferred metacognitive strategies most and cognitive strategies least; (c) less successful learners benefited from cognitive strategies most, with minimal use of metacognitive and memory strategies; and (d) both successful and all learners were found to be medium strategy users though less successful learners reported lower strategy usage overall. Chi-square analysis results further highlighted significant differences between successful and less successful learners in their strategy use frequency.