The geochemical components of the leachate from loess-paleosol deposits can provide information about climate-related post-depositional processes. For example, leachate lithium ([Li]leachate) is a potential paleoclimate proxy because lithium is a typical lithophile element that is readily adsorbed by clay minerals during weathering and pedogenesis, and thus stratigraphic variations in [Li]leachate can reflect these processes. We investigated the [Li]leachate values of two loess-paleosols profiles (the Luochuan and Weinan sections), on a north–south climatic gradient on the Chinese Loess Plateau. Independent paleoclimate information was provided by measurements of magnetic susceptibility, grain size, Rb/Sr ratios, and clay mineral content. During the last glacial-interglacial period, [Li]leachate increased from 0.39 to 1.97 μg/g at Luochuan and from 0.67 to 2.45 μg/g at Weinan, mainly due to increasing pedogenesis. Based on these results we developed a conceptual model to explain the variations in [Li]leachate. Li+ within loess layers is mainly derived from dust input and the decomposition of primary minerals, influenced by the East Asian winter monsoon, while in paleosol layers Li+ is mainly derived from clay mineral adsorption during pedogenic processes, influenced by the East Asian summer monsoon.