Over the years, there has been a great deal of research conducted on the role of tasks in second language acquisition, but less is known about how tasks affect listening comprehension. The present study is an investigation of the impact of task complexity on Iranian EFL learners’ listening comprehension across aptitude. For this purpose, data was collected from two EFL classes including 70 Iranian EFL learners (F=45, M=25). Test-takers' aptitude was assessed by Oxford language aptitude test. Two task dimensions, i.e., planning time and prior knowledge, each under two +/complex & -/simple conditions (i.e., task manipulated for complexity and simple task) were used in test-takers' listening performance. Descriptive statistics, ANOVA test were utilized to analyze the listening performance of the participants. The results of the study indicated that the subjects’ performance was better under simple conditions than complex ones for all task dimensions. Moreover, the results didn’t show any significant difference among performance of the different aptitude levels under both simple and complex conditions. In short, this study didn’t show any considerable effect of aptitude on task complexity.
