Electoral rules and constitutional structures can influence the level of political corruption. We show that proportional representation (PR) systems are more susceptible to corrupt political rent-seeking than plurality systems. We argue that this result depends on the different loci of rents in PR and plurality systems, and on the monitoring difficulties faced by both voters and opposition parties under PR. We also examine the interaction between electoral rules and presidentialism. We test our main predictions and interaction effects on a cross-section of up to ninety-four democracies. The empirical findings strongly support our hypothesis that PR systems, especially together with presidentialism, are associated with higher levels of corrupt political rent-seeking.