Party system nationalization, defined as the extent to which national parties receive similar vote shares across regions, has a huge impact on the nature of programs and policy outcomes from party systems. Nationalized party systems are characterized by nationalized broad based policies and programs while less nationalized or regionalized party systems are associated with more particularistic, pork-barrel based policies and programs. Since party system nationalization affects the nature of programs and policy outcomes, I examine whether party system nationalization does have any impact on the occurrence of ethnic rebellion. I argue that party system nationalization affect the occurrence of ethnic rebellion based on the geographic distribution of ethnic groups. Party system nationalization tends to increase rebellion by concentrated ethnic groups, while it decreases the rebellion by dispersed ethnic groups. I use a dataset of 33 countries over the period of 1985-2006 to test these interaction effects. The findings suggest that party system nationalization increases the likelihood of rebellion of concentrated majority groups, while decreasing the likelihood of rebellion of widely dispersed groups. I also find that party system nationalization have no impact on the probability of rebellion of urban groups and concentrated minority groups.