The Parque Nacional da Serra do Divisor (PNSD), renowned for its remarkable biodiversity, is a conservation unit of the Amazon biome situated at the westernmost limit of the Brazilian territory. However, the PNSD fauna is still poorly documented for most taxa. This study aimed to list the ant species (Hymenoptera: Formicidae) of the PNSD, comparing its diversity found with studies conducted in other hotspots of biodiversity of the world. Field collections were conducted in the northern region of PNSD for four days in 2016, using three collection methods: epigaeic pitfall traps, Winkler extractors, and hand collections. Even with the short sampling period, an impressive number of 261 species of ants were recorded, representing one of the highest richness documented for ants with the least sampling effort applied in a single locality worldwide. Of these species, 66 were newly recorded in the state of Acre, with six representing first-time records for Brazil. These findings highlight the critical importance of the PNSD as a strategic area for ant conservation, both in Brazil and globally.