Detailed magnetic analyses of samples from the Jiuzhoutai well section on the western Chinese Loess Plateau reveal high-resolution signals of summer monsoon change. The last interglacial period is represented here by the 8-meter thick S1 paleosol complex. We have used low-temperature remanence studies to analyze variations in the concentration of superparamagnetic (SP) grains, which previous studies have shown to be largely of pedogenic origin. The SP concentration, interpreted as a proxy for the extent of pedogenesis, shows millennial scale variations within S1. We conclude that the last interglacial period in Asia was characterized by rapid climate fluctuations, with at least one brief return to near-glacial conditions in the middle of oxygen-isotope substage 5e.