The Pampa is a biome shared by Argentina, Brazil, and Uruguay. Despite its high biodiversity, little is known about the invertebrate fauna. The few inventories done so far were conducted outside protected areas, which could result in underestimated real biodiversity. Thus, species inventories from protected areas should be done to serve as reference for conservation. Here we survey the butterflies occurring in the Banhado dos Pachecos Wildlife Refuge, Uruguayan Savanna, Brazil. Sampling was performed between April 2012 and March 2013. After 288 hours of sampling, 1,508 individuals from 113 species were sampled; five new species records for Rio Grande do Sul state and 12 for the Uruguayan Savanna were found. Richness among families was compared to other inventories and butterfly conservation discussed concerning the conversion of grasslands into croplands/pastures. The evidence presented supports that the Pampa is a fragile environment under the pressure of habitat conversion. Biodiversity studies in fragmented areas are needed to provide essential information for conservation programs.