The purpose of the study is to compare the nature of teacher talk between the native and non-native speaking professors with its focus on language functions and interaction modifications in English-mediated writing instruction. The study analyzed the classroom languages of two professors who were teaching college-level composition courses using the same textbook and syllabus. The classes taught by the two professors were videotaped, transcribed, and analyzed based on the AS-unit. The results showed both professors used all of the five functions in the order of information, suasion, opinion, future plans, and checking. The NS professor, on the other hand, used the information function more often, while the NNS professor relied more on the suasion function. The data also displayed that the NS professor gave more feedback responses, whereas the NNS professor asked more clarification requests and repeated their own utterances. The findings implied that the types and distribution of the teacher talk may be influenced by the subject-matter and the instructional foci of each professor.