This study was designed to explore the relationships between L1 (first language) literacy and its lower skills (literal, inferential, and critical comprehension skills) and L2 (second language) reading ability in the Korean EFL context. The contribution of each L1 comprehension skill to explain L2 reading ability was also measured. For this study, 108 Korean middle school students were chosen as participants, and their L1 comprehension skills (literal, inferential, and critical), L2 linguistic knowledge (vocabulary and grammar), and L2 reading ability were assessed and analyzed. Results show that all variables in this study were significantly related to L2 reading ability, but L1 comprehension skills (literal and critical comprehension skills, in particular) were more predictable than L2 linguistic knowledge in explaining L2 reading ability. Therefore, in order to properly understand L2 reading ability, it is necessary to take a closer look at L2 learners’ L1 reading comprehension skills other than various L2 induced factors.