Based on investigations and previous documents, 647 weed species in Jiangsu, Zhejiang and Shanghai, China, were confirmed. Their 32 botanical and ecological characters, which include invasiveness, type of life cycle, seed or fruit size and production, breeding system etc., were collected. 647 weed species were quantitatively divided into 11 groups using the method of cluster analysis. The relationships of their invasiveness with other 31 characters were analyzed employing the GLM and correlate procedure of SPSS 13.0. The results showed that, when the 647 species were regarded as a whole, the species with the characters such as taproot or tuberous roots, unisexual flowers, big seeds (or fruits), zygomorphic flowers, perennial type, mesic or shade habitats are often of lower invasiveness, while those with much seeds (or fruits), growing in the sunny or hygrocolous habitats are probably of higher invasiveness. However, if the weeds of different groups were analyzed separately, the relationships between invasiveness and characters vary with different weed groups. That is, a character, which correlates closely with invasiveness in one weed group, probably does not in other groups. Therefore, it may not reasonble to find a universal index system to evaluate invasiveness of all alien plants in a given area.