• δ 11 B of paleorainwater (δ 11 B pr) in loess-paleosol deposits from NE China are reconstructed. • Kinetic isotope fractionation explains the linkage of δ 11 B pr to the intensity of summer monsoon. • The δ 11 B pr can be employed as a robust proxy for intensity of East Asian Summer Monsoon. • Increase of ice volume in Northern Hemisphere drove an abrupt EASM weakening in NE China at ca. 430 ka. Based on a study of the boron (B) isotope geochemistry of the loess-paleosol sequence of the Niuyangzigou section (NYZG) in Northeast (NE) China, the boron isotopic composition of paleo-rainwater (δ 11 B pr) is used for the first time as a potential proxy for tracing changes in the East Asian summer monsoon (EASM) since the mid-Pleistocene. The acid-soluble phase of loess in NE China, which is characteristically a sandy loess, has lower boron concentrations (0.26 to 0.89 μg/g) and more positive δ 11 B values, from −12.1‰ to +9.4‰, compared to the loess of the Chinese Loess Plateau (CLP). According to the mass balance of boron accumulation from three distinct sources, a mathematical inversion calculation is used to quantify the proportion of boron from each source and to capture the original δ 11 B pr signature. The resulting δ 11 B pr values range from +6.8 ± 0.95‰ in loess layers to +17.3 ± 3.32‰ in paleosol layers, and the boron accumulated in loess-paleosol layers is shown to be mainly from atmospheric precipitation and silicate weathering. Synchronous variations of reconstructed δ 11 B pr and other loess-based proxies, both in NE China and in the CLP, are observed over a large spatial range and on several temporal scales. The linkage of δ 11 B pr to the intensity of the EASM is attributed to the kinetic boron isotope fractionation associated with vapor-precipitate phase separation along the transport path of moisture-bearing air masses. A Rayleigh fractionation model is proposed to interpret δ 11 B pr in terms of the proportion of water vapor loss after multi-step fractionation processes, which is independent of temperature. The monsoon record based on δ 11 B pr shows a significant shift at ∼430 ka, implying an abrupt weakening of the EASM after the Mid-Brunhes Event (MBE), which provides evidence for regional disparities in monsoon evolution in response to the MBE. The ice volume in Northern Hemisphere is a possible factor controlling changes in the EASM in NE China over the past 800 kyr. [ABSTRACT FROM AUTHOR]