The aim of this study is to present the first record of a diving beetle from in late Pleistocene beds of Buenos Aires Provincetle from in late Pleistocene beds of Buenos Aires Province, and to provide new data on the paleoenviron- mental conditions prevailing in the region at that time. Fossil record of the Hydradephaga. The first record of the family Dytiscidae dates from 120 million years BP (Crowson, 1975). Whereas hydradephagans are known from the Late Triassic of Eurasia (Triaplus Ponomarenko, 1977), dytiscids are actually rather rare in the Mesozoic (Grimaldi and Engel, 2005). Probably, the oldest truly dytiscid is Cretodytes Ponomarenko, 1977, from the Turonian (Late Cretaceous) of southern Kazakhstan. Most of the published Cenozoic records of aquatic beetles originate from the classical palaeontological localities in Europe (i.e., Fikáček et al., 2008 and references therein). Cenozoic fossil Hydradephaga seem to be all Dytiscidae and Gyrinidae of modern types(Crowson, 1975), and have been cited from Quaternary sediments of Japan, Korea, Sakhalin island, eastern Siberia, Australia (Elias, 2010), North Greenland (Böcher, 1995), and now Argentina.Fil: Ramírez, Leonardo César. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Austral de Investigaciones Científicas; ArgentinaFil: Michat, Mariano Cruz. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Biodiversidad y Biología Experimental y Aplicada. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Biodiversidad y Biología Experimental y Aplicada; Argentina