The evolution of Sino-North Korean relations is an interesting historical phenomenon worth careful reexamination. The diplomatic documents recently declassified by the Chinese government shed new light on this old issue. Based on previous research and new information, the author finds that Sino-North Korean relations were closely related to Soviet-North Korean relations: The two sets of bilateral relations ran in opposite directions. Moreover, the rise and fall of North Korea’s relations with China were determined by the political division on the Korean peninsula and Sino-Soviet polemics, and in the competition for influence between ideological and security concerns, the latter won out. Throughout, North Korea was not weak; it was in control of its relations with its two major allies.