This study is about the effect of English as L2 on teaching and learning Chinese as L3. It focuses on Korean learners’ recognition and learners’ corpus. Korean learners usually learn English before learning Chinese. Thus, their L1 is Korean, L2 is English, and L3 is Chinese. As for the learners’ recognition, a survey was conducted, which had 4 questions asking the learners’ background and 9 questions asking what the learners think about the effects of L1 and L2 on learning L3. As for the learners’ corpus, the learners’ writings were collected from ColloConc, and 245 sentences were analyzed. The sentences were classified into 6 types according to how English affected the learners’ writings, and some typical types of sentences were presented in this paper.