Oriental Chaco, part of the Great American Chaco, embraces a plain area with soft slopes towards the west-east region. In this region, different kinds of landscapes and vegetation converge, both conditioned by topographical and pluviometric gradients. This region undergoes processes of fragmentation and habitat loss due to intense human activities such as deforestation, agricultural exploitation, construction of a dam, and pollution. In order to contribute to the knowledge of the Oriental Chaco biodiversity, we studied the herpetofauna during one year. We sampled four sites between the coordinates 25° 00' S, 58° 00' W and 27º 00' S, 61º 00' W in the provinces of Chaco and Formosa. Eighty-eight species were registered in the studied places. The higher biodiversity was in grid 46.