Among the physiographic regions included in the central South American diagonal of open formations, the Chaco, with some endemic species, represents the southernmost dry area. In Brazil, the Chaco is found in southwestern corner of Mato Grosso do Sul state, mostly in the municipality of Porto Murtinho along the Paraguay and Apa rivers. From February 2008 to December 2009, we carried out an inventory of amphibians and reptiles in Porto Murtinho, using pitfall traps, time-limited searches, and occasional encounters. A total of 34 amphibian and 39 reptile species were registered. Although some typical Chacoan species were found, most of the species are open area dwellers that also occur in other open biomes, such as the Cerrado and Caatinga.