The Eocene-Oligocene boundary (EOB) marks a period of dramatic global climatic change correlated with pronounced mammalian faunal change. The timing of these events is well constrained in North America and Europe, but the Asian record has yet to produce a synthetic section linking environmental change, mammalian fossils, and precise geochronological dates. Here we present the first magnetostratigraphic section for the Hsanda Gol Formation, Mongolia, which yields significant Oligocene fossils and also marks a pattern of aridification that is tightly correlated to the EOB (33.9 Ma), supporting a broader pattern of aridification in the central Asian plateau across the EOB. Oligocene faunas of Asia can now be confidently correlated to those of North America, Europe, and Africa. These results suggest that mammalian faunal turnover within Asia occurred slightly later than similar events within Europe, and question the influence of Asian immigrants on the Grande Coupure faunal turnover.