Lepidoptera is one of the four megadiverse insect orders, comprising butterflies and moths. In Brazil, the bulk of knowledge about the butterfly fauna is restricted to some areas in the southeast of the country, with large gaps of knowledge in other areas. The state of Mato Grosso is one of the largest states in Brazil, and holds three of the main Brazilian biomes: Amazon rain forest, Cerrado and Pantanal. However, knowledge about Mato Grosso butterflies is fragmented and restricted to a few localities, and information is scattered in various sources. The aim of this study is to assemble the biodiversity information of the butterfly fauna of the state of Mato Grosso based on historical and recent literature data and collections carried out in the southwest of the state from 2007–2009. Records without precise locality data or taxonomic information were not included. Species identification was based on literature and comparison with specimens in collections; higher and species-level taxonomy were updated based on the Neotropical Checklist of Hesperioidea and Papilionoidea and recent phylogenetic and revisionary taxonomic works. In total, 901 species were recorded in 2,820 occurrence records. This represents 148 species of Hesperiidae, 29 Papilionidae, 28 Pieridae, 77 Lycaenidae, 238 Riodinidae, and 381 Nymphalidae. Of these, 207 species records are from the type specimens of species described in the state. Based on the results and literature records for other Brazilian states and biomes, probably the figures for Mato Grosso are underestimated, particularly in the families Hesperiidae, Lycaenidae and Riodinidae, in that order. Future collecting efforts should be directed towards certain areas of the state, especially in less sampled areas and biomes, as the north of the state and Pantanal.
