Abstract Maritime disputes among the East Asian States have garnered increasing attention worldwide with expanding offshore activities in the East China Sea. To avoid confrontation and potential conflict, unilateral maritime claims in the East China Sea usually have been non-explicit. While maritime boundary disputes remain unresolved in the region, changes have taken place because of resource shortages, the rise in military assertiveness from Tokyo, and increased alliances with the United States. This article explores the limits of unilateral activities within the disputed maritime area under current international law and how East Asian States should behave when they encounter unilateral activities conducted by other States, including analysis on sovereign entitlement and the limits of unilateral activities in the region. A code of conduct among the East Asian States is needed to ensure peace and prosperity in the region.