As verbs have a central role in sentence construction and sentence processing, it is necessary to know which verb characteristics influences readers’ speed and accuracy, specifically while reading foreign language sentences. To this aim, we investigated the effects of verb argument structure (VAS) complexity through verbal subcategorization and thematic options. We also wanted to assess whether these VAS features interact with the proficiency levels of Iranian EFL learners (intermediate and advanced). After administering the Oxford Placement Test (OPT) to measure the participants’ proficiency-levels, we conducted a self-paced reading task involving reading sentences followed by comprehension questions to collect reading times and response accuracy rate. Sixty-six healthy Iranian adults participated in the experiment. The reading times from the four regions starting with the verb as the critical regions were analyzed using the linear mixed-effects regression and ANOVA. The behavioral performance of the participants reflected increased sentence processing cost and decreased accuracy as a result of VAS complexity. Specifically, the higher number of subcategorization frames and thematic options led to slower reaction times and more incorrect responses to the reading comprehension questions by the learners. Although the participants’ proficiency-levels did not significantly affect their sentence processing pace, its impact on the accuracy was significant. These findings emphasized the importance of considering VAS features as a determinant factor in processing sentences. Hence, verbal characteristic should be taken into account in structuring instructional materials for EFL learners, so that verbs would be taught based on their VAS complexity, staring with the simplest structures.