The paper discusses the Paleogene and Neogene stratigraphy of Siberia and estimates the paleotemperature and precipitation trends. The paleotemperatures were estimated on the basis of climatograms (V.P. Grichuk) and the analysis of temperatures in the ranges of the main plant genera. The Paleogene and Neogene temperatures were always high (at least 0° C). The average annual temperatures varied from +20 to +10 – +5 ºC, the winter temperature being from +10 to +5 – +3 °C. The precipitation varied from 1400–1000 mm/yr in the Paleocene and Eocene to 800–500 mm/yr in the Oligocene and 250–100 mm/yr in the Late Miocene. The climate cooled in the Late Eocene–Early Oligocene, Late Oligocene–Early Miocene, and Early Pliocene. Three stages of arid climate have been distinguished: one in the Late Miocene (7–5.5 Ma) and two in the Early Pliocene (Cherlak and Bitekei time). In the Late Pliocene (2.6 Ma, Kulunda Horizon), the cooling was slight. It gave rise to vegetation zones, which were distributed similarly to the present-day ones. The arctic flora migrated to the southern West Siberian Plain at 1.65–1.8 Ma (Ubinskoe–Erestnaya time), when the climate was close to a glacial one.