This study investigates the way Korean learners resolve English relative clause attachment ambiguities in the of-condition and with-condition. Therefore, the focus of this study is to decide whether English native speakers and Korean learners differ with respect to sentence processing strategies and language development stages can influence Korean learners’ sentence processing strategies. The study was conducted in three different stages of language development(middle school, high school, and university). Subjects took tasks with Korean and English sentences containing ambiguous relative clause attachment. The findings indicated that first, Korean learners in this study transferred Korean processing strategy to English sentence processing in the of-condition. So Korean learners had the processing strategy that was different from that of English native speakers. Second, Korean leaners depended on the lexical information in the with-condition, which means Korean learners used a universal processing strategy like English native speakers. Third, according to language development stages, there was a gradual change of the processing strategy to depend on a language-specific strategy(native language strategy) more and more in the of-condition, whereas there was no change in the processing strategy in the with-condition.