A high resolution pollen record from Maili Bog, Horqin sand land, central Norhteast China, shows that the open sand land forests around the bog have continuously delined since 3100 a B.P., and the main herb taxa have experienced consistent rise in abundance. The most significant changes were in the pollen percentages and pollen concentration of Quercus mongolica, Artemisia and Chenopodiaceae. Furthermore, the changes of the herb pollen generally lagged behind those of trees, and the rise in Chenopodiaceae seems to follow that of Artemisia. It is thus possible that the stable sand dunes covered with open forest were first turned to partly stable sand dunes with Artemisia as the dominant taxa, and this was followed by the change from partly stable sand dunes to mobile sand dunes which usually support only Chenopodiaceae. Archaeological relics and documentary records show an increased human population and agricultural activities in this region beginning from Gaotaishan Culture (3300-3000 a B.P.). The farmers may have come from the southern regions of Liaoning Province, which was in turn influenced by the advanced agriculture of the middle and lower reaches of the Yellow River. The above mentioned vegetation changes in the Maili region, therefore, may have been mainly induced by the human interference with the sand dune system. This inference is generally supported by charcoal count data from the pollen profile, the different changes in pollen between extra region Pinus and intra region Quercus, and pollen data from the other sites in Northeast China. It is thus obvious that caution should be taken when one reconstructs the late Holocene climate changes using pollen data in such a region. It is also suggested that the past reconstruction works of the middle to late Holocene climates in some regions of the country may need to be re assessed.