High-resolution analyses of terrestrial mollusks from two loess sequences in the Chinese Loess Plateau provide continuous evidence of paleoecosystem and paleoclimate processes through the recent three glacial-interglacial cycles. Systematic fluctuations in thermal-humidiphilous mollusk type (Punctum orphana) indicate that the strength of the SE Asian summer monsoon is sensitive to orbital forcing at the obliquity and precession periods (41 and 23 kyr, respectively). In contrast, the cold-aridiphilous mollusk (Vallonia tenera and Pupilla aeoli) variability displays a different pattern. The strongest powers are centered at about 100 kyr and 41 kyr periods, which drive the major period of winter monsoon variations in the Chinese loess. These different responses to winter and summer monsoon in the Loess Plateau of China suggest that both of these monsoon systems are tightly coupled in the 41 kyr cycle, but are not coincident relative to the precession (19--23 kyr) and 100 kyr cycles. The relationship between the winter and summer monsoons is not a simple model reflecting a seesaw pattern. ¿ 2001 American Geophysical Union