Extensive loess deposits that mantle on various landscapes are found in the adjacent areas of the Horqin and Otindag dune fields,which should record the aridificaion history and desert evolution in Northeastern China.Here,we present a high-resolution grain-size analysis of a 59.9-m-thick loess-paleosol sequence in the south margin of Horqin and Otindag sand fields that covers the ca.1.08 Myr(1 080 kyr).The grain-size distribution of these loess deposits shows typical features of aeolian deposits,and records the cyclical variations of the East Asian winter monsoon and dune fields during glacial-interglacial cycles.It also demonstrates a long-term drying trend caused by the strengthening East Asian winter monsoon in Northeastern China since ca.1.08 Ma.The Horqin and Otindag dune fields expanded in ca.670 ka and ca.943 ka.These drying events correspond with other records in the western and central China.It may reflect that the increase of northern hemisphere ice volume and global cooling should have forced the stepwise aridification and caused dune field extension to the Southeast China since the Mid-Pleistocene Transition Event.