The Security Dilemma in Sino-Japanese Relations by LEE Yu Pan Master of PhilosophyEven though economic relations between China and Japan have improved in recent decades, their security relations raise the prospect of clashes due to the perceived incompatibility of their interests, as manifested for example in territorial claims and rivalry for energy resources. This thesis analyzes the two states' security relations using the "security-dilemma" and "constructivist theories" of international relations.The security dilemma is a condition in which states' attempts to increase their own security, out of the mutual fear and suspicion, results a decrease in security for all. The constructivist theories suggest that the identities of actors, social norms, states' interests and government policies are inter-linked in both domestic and international politics; each component thus shapes and then reshapes others.International relations should not be understood by merely analyzing material capacities.In order to understand the security relations between China and Japan, it is imperative to investigate the threat perceptions of various actors within both states, including the general public, the political leadership, the military, the academics and other sub-state actors.By employing the mentioned theories, it is found that the general public in both states are the key sources to consider the other as a security threat. Fear or resentment among states, which might initially be constructed by the behaviors or policies of other actors, would in turn further shape or limit other actors' perceptions and interests. The public also put constraints on their governments' freedom to maneuver diplomatically and to adopt policy choices, it thus affects the security relations between states. The thesis concludes that deepening interactions between people in both state and carefully conducted diplomatic behaviors, such as choice of wording in reconciliation actions and joint action by states' leaders at symbolic occasions or locations etc, can be the key of preventing the security dilemma from escalating. As a result, in the case of Sino-Japanese relations, the security relations cannot be improved by deploying military means. DECLARATIONI declare that this an original work based primarily on my own research, and I warrant that all citations of previous research, published or unpublished, have been dully acknowledged.