Author(s) Hojun Lee Keywords Procedural reform, presidentialization, procedural cartel theory, presidential faction, South Korean National Assembly Abstract The common assumption of legislative politics is that the majority party structures procedural rules to suit its interests. In a presidentialized context, however, presidential electoral incentives prevail over majority party’s incentives when voting on procedural rules changes and the threat of punishing majority-party defectors is not credible when those defectors vote with the presidential candidate. To test these claims, I analyze the case of the procedural reform in the South Korean National Assembly. The case study reveals that 1) the leading presidential candidate of the ruling majority Saenuri Party compromised on the procedural reform bill that imposes restrictions on the majority party’s cartel arrangement due to presidential electoral incentives; 2) a significant number of Saenuri Party members defected from the majority of their co-partisans to vote with the presidential candidate; and 3) career advancement ratio and re-nomination ratios demonstrate that those defectors were not punished afterwards. Author(s) Bio Hojun Lee is a Ph.D. candidate in Political Science at the Department of Political Science and International Relations, Korea University, South Korea (hjlee87@korea.ac.kr). He is currently working on his dissertation, tentatively entitled “Party Government in the South Korean National Assembly,” which examines how party government operates in the South Korean National Assembly. His articles have appeared in peer-reviewed journals such as Government & Opposition, Korean Journal of International Studies, Korean Journal of International Relations (in Korean), and Journal of Parliamentary Research (in Korean). DOI: https://doi.org/doi:10.1017/jea.2018.31