AbstractA survey of species and distribution of exotic weeds was conducted with the square plot method in different habitats in Nanjing. The collected data were analyzed with principal component analysis(PCA).  Twenty-one exotic weed species belonging to 19 genera and 11 families were recorded in autumn in the region, and of them originated from America. Composite comprised the most species among all families. The results of principal component analysis showed that the most important factors affecting the occurrence and distribution of exotic weed species were the levels of human disturbance and soil humidity. According to these two factors, all samples were divided into four groups. The dominant exotic weed species in each group were regarded according to the importance value of the species. Group Ｉ included samples collected from dry land, and its dominant exotic weed species were Amaranthus retroflexus,Veronica persica and Alternanthera philoxeroides. Group Ⅱ included samples located in wastelands and right-of-ways which were non-managed or non-irrigated farmland. The dominant exotic weed species mainly belonged to composites, such as Erigeron annuus,Conyza bonariensis and Conyza canadensis. Group Ⅲ included samples located in public parks where the number of exotic weed species was abundant. The dominant species were Ambrosia artemisiifolia,Plantago virginica,Alternanthera philoxeroides,Aster subulatus,Erigeron annuus,Conyza bonariensis,  and Conyza canadensis. The last group was mainly composed of samples distributed on the waterside and in paddy fields. The dominant exotic weeds were Alternanthera philoxeroides,Aster subulatus and Medicago hispida. The analysis of the difference of species richness among groups showed that invasion of exotic weeds had a harmful influence on biological diversity. Some suggestions for management of exotic weeds are proposed.