Using structural equation modeling analysis, this study examined the contribution of vocabulary and grammatical knowledge to second language reading comprehension among 190 advanced Chinese English as a foreign language learners. Vocabulary knowledge was measured in both breadth (Vocabulary Levels Test) and depth (Word Associates Test); grammatical measures focused on learners' implicit (timed grammaticality judgment task), as well as explicit knowledge (grammatical error correction task); reading comprehension had three indicators, namely, co-reference, textual inference, and gist. Vocabulary knowledge related significantly to reading comprehension; grammatical knowledge showed a weak contribution to reading comprehension after controlling for the effect of vocabulary knowledge. In addition, learners' implicit knowledge of grammar had a stronger relationship to reading comprehension than explicit knowledge, over and above the effect of vocabulary size. (Contains 3 tables and 1 figure.)