Oxygen isotope compositions were measured in quartz grains extracted from a 7.0 Ma red clay-loess sequence at Lingtai and six late Pleistocene loess sediments(Malan loess). Results show that the changes in oxygen isotope compositions of Malan loess are basically controlled by the geochemical characteristics of the source materials, while the effect of weathering process after dust deposition could be minor. The oxygen isotope distribution of quartz grains from red clay at Lingtai is similar to that of the overlying loess-paleosol sequence, thus indicating that the red clay at Lingtai has the same eolian origin as the loess-paleosol deposits. Furthermore, the oscillations of the isotope compositions in 4-16 μm-sized quartz grains may reflect the changes, to some extent, of the climatic systems of the source region.