The current study was designed to identify the relative significance of syntactic and lexical knowledge in English as a Foreign Language (EFL) reading comprehension of 254 adult Turkish university students. The role of two dimensions of lexical knowledge, lexical depth and breadth in L2 reading comprehension were also examined in the current study. A Syntactic Knowledge Test (SKT), Reading Comprehension Test (RCT) composed of TOEFL, Vocabulary Levels Test (VLT) and Word Associates Test (WAT) were used in the data collection process. Correlation and multiple regression analyses were utilized to analyze the data. The data analyses showed that all variables of the study positively and significantly correlated with each other. Moreover, all independent variables together significantly predicted RCT scores of the participants. However, when each variable was examined separately, syntactic knowledge was the most contributive variable to L2 reading comprehension. Lexical breadth also significantly explained L2 reading comprehension of EFL learners. The unique contribution of lexical depth to L2 reading comprehension was very low and not significant. Moreover, the independent variables were also correlated with each other. The findings of the current study were compared with the previous findings, discussed and justified in accordance with them. Pedagogical implications were offered.