A 2000-year fossil pollen series from Maili Bog, Northeast China, is presented. In the pollen record, which has a time resolution of 28 years during the last 1000 years, the period 1000--660 yr. BP stands out as unique because it witnessed a remarkably increased pollen accumulation for almost all the taxa. This change could not be explained by the relaxation of human interference stress, because population density and intensity of agricultural activities during Liao and Jin Dynasties (AD 916 to AD 1234) were generally larger than any previous time in the study area. Instead, it may indicate increased summer monsoon rainfall in Northeast China during the time comparable to the Medieval warm period of Europe. The general summer warming over Eurasia relative to the oceans during the period is assumed to be the cause for the strengthened monsoon circulation and increased rainfall in the temperature monsoon area of East Asia. ¿ 1998 American Geophysical Union