The present ex post facto correlational research is aimed at exploring the relationship between grammar and vocabulary knowledge components in L2 reading comprehension. The study focuses on two cohorts of EFL students with different proficiency levels: more proficient (\MP) and less proficient (LP). Two dimensions of grammar knowledge are measured: implicit, through timed grammaticality judgment tasks and explicit, through grammatical error correction tasks. Two facets of vocabulary, viz. depth and breadth, are also assessed by Word Associates Test (WAT) and Vocabulary Levels Test (VLT), respectively. Reading comprehension is also tapped by five indicators of vocabulary, detail and negative factual information, main idea and purpose, co-reference and inference. The data were analyzed through multigroup structural equation modeling, running AMOS. It was revealed that in the MP group, vocabulary knowledge was a better predictor of reading. In the LP group, however, it was unveiled that the role of grammar seemed to be slightly more contributive in predicting reading comprehension juxtaposed with that of vocabulary. Some implications are also discussed at the end.