The present study intended to examine the relationship between working memory (WM) and writing performance of a group of Iranian EFL learners and to explore whether learners with different working memory levels perform differently on the fluency, accuracy and complexity of texts produced or not. The necessary data were collected through the argumentative essay writing prompt and a computerized Persian version of reading span test as a measure of learners’ WM capacity. The correlation analysis revealed that there was a significant positive relationship between these two constructs. The results of Multivariate Analysis of Variance (MANOVA) indicated that there were significant differences between High, Mid and Low WM groups in terms of fluency and accuracy of texts produced, but not their complexity. The findings confirmed the importance of WM while working on cognitively challenging tasks such as writing which requires automation and effective management of cognitive resources while writing. On the whole, the present study confirmed the idea that learners with different learning characteristics orchestrate their mental resources in different ways to perform in different phases of writing and part of their difficulties or even capabilities in writing can be attributed to the efficiency with which they apply these resources while dealing with different writing systems (formulation, execution, or monitoring) or engaging in different writing processes (translating, planning, programming, reading, or editing).
