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Main climatic indexes ( mean January, July and annual temperatures; duration of the frost-free period; seasonal and annual precipitation; and annual potential evaporation) are estimated for the Last Interglacial (Eemian-Mikulino-Kazantsevo-Oxygen Isotopic Substage 5e) climatic optimum in northern Eurasia. Reconstructions are based on the palaeoforistic data from 29 sites. The distribution of temperature deviations from present-day values in northern Eurasia, as well as in the northern hemisphere as a whole, indicates certain areas where temperatures during the Last Interglacial climatic optimum were lower than at present. The greatest positive deviations occurred in the high latitudes and gradually decreased towards mid-latitudes. At about 45 degrees N the mean January temperature was close to that of the present day. For the mean July temperature, the zone with minor deviations is situated further to the north, at 55 degrees N. South of 50 degrees N, an area with small negative temperature deviations from the present-day values is reconstructed. A similar decrease in temperature deviations from high to low latitudes was the general tendency in various warm epochs, including the Holocene and the Eocene optima. In the arid and semi-arid regions of northern Eurasia, a considerable increase in precipitation took place, while air temperatures were close to those of the present or even slightly lower. Another peculiarity of the climate in the Last Interglacial climatic optimum relates to the meridional temperature gradient, one of the factors strongly influencing the intensity of the Westerlies in the mid-latitudes of the northern hemisphere. Our reconstructions for northern Eurasia tend to contradict this rule. The paradox can be explained by a compensation mechanism: a substantial increase in winter temperature in Siberia indicates that the Siberian atmospheric High was weaker and smaller at the Last Interglacial climatic optimum than at present. The reduced role of the Siberian High was compensated by more frequent invasions of the Atlantic air masses from the west, even though the meridional temperature gradient was smaller than at present.