Kim, Serom. 2018. “A Confrontational Discourse Marker I don't know”. The Sociolinguistic Journal of Korea 26(1). 83~109. The literal meaning of I don't know (hereafter IDN) references the speaker's insufficient knowledge about the topic at hand. However, in social interaction, speakers strategically use IDN in non-literal way to accomplish specific interactional goals. Preceding studies have mainly focused on analyzing the ‘avoiding functions’ of IDN in terms of how interactants use it to avoid disagreement or downgrade face-threatening acts. Little attention has been given to addressing the question of how IDN, as a discourse marker, is used in institutional contexts, particularly in news interviews where it is frequently used in responding turns. To address this lacuna, this study, from a conversation-analytic perspective, aims to analyze the interactional functions of IDN in political news interviews. The findings suggest that the confrontational functions of IDN are recurrently observed in the way the interviewee challenges the adversarial nature of questions or confronts the interviewer. In this respect, I propose four functional categories of IDN in regard to the interactional imports it has as a responsive uptake of the interviewer's questions: to confront the interviewer, to resist the terms and agendas of the questions, to disconfirm presuppositions, and to avoid aligning with preference favored by the design of the questions. Implications of the findings are noted with reference to their relevance to future research that approaches IDN as a discourse marker.