In the context of growing US-China tensions, South Korean administrations have opted for degrees of strategic ambiguity, refraining from overt actions that suggest South Korea is taking sides. While strategic ambiguity has been moderately successful, there are limits to this approach which make it unsustainable. This paper will argue that rather, South Korea needs to apply a principled middle power diplomacy, which refers to a middle power carrying out roles expected of it in accordance with a set of rules or values that uphold the liberal international order. The goal of principled middle power diplomacy would be to shape the environment in which the current great power rivalry is unfolding, in order to moderate the fallout of great power competition. After an analysis of South Korea’s middle power diplomacy, this paper will recommend that South Korea double down on its commitment to multilateralism so that it can augment its roles as a facilitator and agenda-setter on the international stage.