Sino-Japanese maritime disputes in the East China Sea concern two issues: the territorial sovereignty of the Diaoyu Islands and maritime delimitation. The sovereignty dispute over the Diaoyu Islands has been an unavoidable, key factor in negotiations on East China Sea issues. The change of legal attitude from median-line to 200 nautical miles distance and the reluctance to admit the fact of sovereignty dispute over Diaoyu islands constitute the main obstacles to the promotion of energy cooperation in the East China Sea. A resolution to the delimitation issue will likely take the form of joint development, further sincere negotiations or international judicial settlement. But judicial settlement may only be possible if the two countries agree to submit their disputes, also a mutually acceptable arrangement over the Diaoyu Islands is essential.