Phonological memory (PM) is viewed as one of the key elements in language learning. The present study was an effort to investigate the relationship between PM, reading comprehension, and vocabulary size of Iranian high school EFL learners. The participants were 58 high school freshmen and senior students. Administering Oxford Quick Placement Test (QPT), the participants were divided into two groups of proficiency, i.e. elementary and lower intermediate. Afterwards, two measures of PM, namely

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... word repetition (NWRP) and nonword recognition (NWRC) tests, a reading comprehension test, and Schmitt's vocabulary levels test were administered. The results showed a significant relationship between reading comprehension, vocabulary size, and PM measures at both levels of proficiency. Moreover, the regression analyses showed that NWRC can be a better predictor of L2 learners' performance on reading comprehension at the lower intermediate level, and NWRC was found to be a better predictor of vocabulary size for both groups of language proficiency.