Hedging is a novel strategy different from balancing and bandwagoning, which has been increasingly employed by many secondary states in the context of the new emerging bipolar system dominated by China and the United States in East Asia since 2008. Among them, South Korea is regarded as a typical hedger. However, empirical evidence demonstrates that South Korea has failed to carry out its hedging strategy in a stable manner. Why does South Korea's hedging show such a strong instability? Under what circumstance does South Korea tend to execute hedging and under what circumstance does not? The existing literature and researches are not sufficient for giving convincing answers to the above puzzles. Therefore, this thesis aims to dig out the reasons for these questions. Following a qualitative methodological research design with case-study and interviewing approaches, this thesis adopts the neoclassical realist framework to analyze South Korea's hedging by combining both the system and unit-level factors. Therefore, this thesis is novel in both content and theoretical approach with practical and theoretical significance. This thesis postulates the system stimuli generated by the emerging bipolar system in East Asia as the independent variable, South Korea's leader image and public opinion as the two intervening variables, and South Korea's response to the emerging bipolar system in East Asia as the dependent variable. Based on this, the thesis put forward the main hypothesis, which outlines the interaction between the intervening variables (leader image and public opinion) and South Korea's hedging. It finds that the leader image and public opinion influence South Korea's diplomatic response. Specifically, the key leaders and public's perceptions and trade. offs of the system stimuli constitute South Korea's internal logic of choosing to hedge, and the dynamics in their perceptions and trade-offs explain the instability of South Korea's hedging. It also presents three other findings in terms of South Korea's domestic politics and hedging, which offer supplements to the main conclusion.