By citing North Korean sources, the South Korean media have recently delivered the news that Kim Jong Il had already chosen his third son, Kim Jong Un, as his political successor in late 2008 or early 2009. He selected a son who was still young and inexperienced.What was the reason behind this decision? This paper attempts to provide a convincing answer to this perplexing question. According to institutionalists, individual actors develop an institution, and the institution in turn affects the actors and restrains their choices. We argue that, among the many political institutions in North Korea, those closely linked to the cult of the Kim Il Sung family are directly related to the logic behind the political succession decision. The institutionalization of the cult of the family provides a justification for political succession in the state. Kim Jong Il has been one of the chief architects of the institutionalization of the cult, and the institutionalization in turn has limited his choice in selecting his successor, leading to the recent dynastic decision.