Abstract Piauí, a Brazilian Northeast state, has been considered one of the most important regions for the presence of new taxa in ants globally, especially considering the ecosystems’ diversity formed by the transition of the three biomes in the state, the Cerrado, Caatinga and the Atlantic Forest. Despite the recent increase in studies of ant diversity in the Neotropical region, Piauí still represents a major knowledge gap regarding its ant fauna. Therefore, this study aimed to increase the knowledge about the ant fauna of the state by generating a list of species with data obtained from the literature, online repositories and collection expeditions to the Serra da Capivara and Serra das Confusões National Parks. A total of 152 species in 52 genera and nine subfamilies were registered from 24 localities in Piauí. Fifty-eight out the 152 species recorded represent new records for the state, eight are new records for the Brazilian Northeast Region, and one consists of a new record for the country. Eleven species are here recognized as new for science. Considering the field expeditions carried out here, this work represents the first standardized study for the ant fauna of Piauí. The species list presented considerably exceeds the current number of species registered for the state so far. From the present 48 records, the number of species for Piauí raises to more than 150 with a tendency to increase with the accomplishment of future field endeavors and advances in the study of the local ants.