This study was designed to highlight the potential effects of different types of Explicit Syntactic Markers (ESMs) on the sentence comprehension of EFL learners of different age-range and proficiency levels. Consequently, two hundred and forty beginners, intermediate, and advanced Iranian EFL learners were selectedfrom an initial pool of six hundred and sixty learners. They were selected based on their McMillan Placement Test (MPT) performance. Subsequently, they were categorized into two age groups teenagers and adults. An online software application (Com-Chron) was utilized to provide learners with a set of ESM and non-ESM English sentences on the screen to measure the accurate comprehension and the elapsed time needed for the perception of the presented sentences. Data analyses revealed that participants had a significantly superior performance for comprehending the ESM items (though they were longer sentences than non-ESM items). Furthermore, it was revealed that proficiency level, unlike age, caused a statistically significant difference in comprehending the ESM sentences. It was also concluded that different types of explicit syntactic markers imposed different degrees of comprehension difficulty both in terms of accuracy and the needed time for the participants’ comprehension; sentences with punctuation marks and conjunctions were the easiest for the participants, while those including determiners and link breaks were the most challenging. Results also indicated that all the ESMs (except for the link breaks) can significantly account for English sentence comprehension and can be assumed as comprehension predictors to various degrees .