The empirical research was examined for a sample of 129 4th graders in an EFL environment in order to explore the fundamental elements impacting on second language (L2) reading comprehension and their structural relationship to L2 reading comprehension. The materials used for the current study were (1) a questionnaire on L2 reading comprehension, (2) L2 productive/receptive vocabulary test and (3) L2 reading comprehension test, adopted from Woodcock-Johnson Ⅲ Diagnostic Reading Battery (Woodcock, Mather, and Schrank 2004). First, four factors on L2 reading comprehension were unveiled: L2 reading comprehension learning strategy, first language (L1) proficiency, parents’ interest on their children``s English learning, and extra-curricular activities. Those factors are strongly associated with L2 vocabulary and L2 reading comprehension. Second, L2 productive/receptive vocabulary were significant indicators of successful L2 reading comprehension. Finally, L2 vocabulary knowledge contributed a significant amount of unique variance to L2 reading comprehension based on the structural equation modeling (SEM). These findings are steadily aligned with the Lexical Quality Hypothesis in which L2 vocabulary knowledge is assumed to be a critical determinant of L2 reading comprehension (LQH: Perfetti & Hart, 2001).