The use of code-switching to Chinese is a prevalent phenomenon in EFL classrooms in China. Using a framework based on Auer’s Conversation-Analytic theory (1984, 1995), this thesis examines the use of code-switching in two senior high school classrooms in Lixian County where students in rural areas of southern China study English as a foreign language. More specifically, this thesis attempts to explore the nature of classroom discourse and the role of code-switching from teachers’ perspectives as well as to investigate students’ attitudes and expectations about teachers’ language use. A particular focus is on how teachers and students use more than one language to refer to a monolingual textbook in fulfilling lesson objectives, and another one is interaction between teachers and students. This research adopts both qualitative and quantitative methodologies, and the data were collected from a Senior 1 and a Senior 2 English classroom. Two English teachers, one experienced, one novice, are involved in this research, and the credibility of this research is built on several data collection methods, including classroom observation, audio-recordings (fourteen recordings in total), the author’s field notes, interviews, and a survey of students. It is found that teachers take advantage of code-switching to Chinese (Putonghua) to accomplish their teaching objectives. Both teachers seem to have sufficient knowledge and capacity to teach English mostly in the Target Language (TL) or in a mixed code. It is only for the purpose of effective teaching that they choose to use Putonghua, either to achieve optimal teaching effect, to foster a healthy and ii intimate teacher-student relationship, or to cultivate students’ proper emotional attitudes and values towards study or life. Accordingly, students also hold that appropriate code-switching is beneficial to their English improvement and their learning efficiency in the classroom, but in the meantime they also desire to be exposed to more input in English in the classroom.