Scholars and policy makers have intensely debated institutional reforms of the United Nations (UN) since its creation. Yet, relatively little attention has been given to institutional design preferences among the public in UN member states. This study examines two questions: Which possible rules concerning UN authority and representation do citizens prefer? Which personal and country characteristics are associated with their varying institutional preferences? A population-based conjoint survey experiment conducted in Argentina, China, India, Russia, Spain, and the United States is used to identify public preferences on nine distinct institutional design dimensions figuring prominently in UN reform debates. We find widespread support for increasing or at least maintaining UN authority over member states and for handing control over its decision-making to UN organs that would represent the citizens of every member state more directly. Citizens’ institutional preferences are associated with their political values and vary depending on whether their home countries would gain or lose influence from a specific reform.