This research is a descriptive qualitative research which has a purpose to uncover the diplomatic representation of South Korea towards North Korea by using the study of assertive speech-act. The data of this research are speech videos of president Moon Jae-In taken from YouTube with its transcription and were carefully examined using speech-act classification that was suggested by Searle and Korean assertive speech-act verb classification proposed by Jang. Two international relations experts were also interviewed to strengthen the representation data in terms of its political implication.The result of this research shows that the assertive verb & function of 합의하다'habeuihada' (agreeing) dominates in President Moon Jae In's speeches. Based on the result of the interviews with international relations experts, the assertive speech acts of President Moon Jae In do represent the diplomatic state and attitude of the two Koreas, the benefits and the losses, as well as the influence of United States of America in the diplomacy done by South Korea towards North Korea.