We studied the small mammal assemblage (bats, marsupials and rodents) of Parque Nacional Chaco and Capitán Solari(Chaco Province, Argentina) based on captures and analysis of owl pellets. Twenty-one species were recorded during abrief survey, including two marsupials, seven bats, and twelve rodents. In addition, we documented the first occurrenceof the bat Lasiurus ega in the Chaco Province, and extended to the southwest the distribution of the didelphid marsupialCryptonanus chacoensis and the oryzomyine rodent Oecomys sp. We also provided a second occurrence site in theHumid Chaco for the cricetid rodents Calomys laucha and Holochilus brasiliensis. Identified taxa belonged to speciesthat are typical of the Humid Chaco ecoregion of Argentina.