Abstract: Xanthium strumarium L., the fruits of which are used as a remedy for rheumatoid arthritis and rhinitis in traditional Chinese medicine, is a common weed distributed all over China. The present paper deals with a study of the chromosome numbers and karyotypic analysis for X. strumarium. The seeds used for examination were collected from 30 habitats belonging to 20 provinces and autonomous regions of China. The number of chromosomes in root tip cell has been found to be 2n=36, in accord with those reported by many previous authors. However, aneuploidy with 2n = 34 and 35 within individual plant is of frequent occurrence.In the light of chromosomal terminology defined by Levan and al., the karyotype formula of X. strumariura is 2n = 36 = 26m + 2m(SAT)+8sm, and belongs to Stebbins' "2B" type of karyotypic asymmetry.The cytological information obtained through the present study does not give support to the specific segregation of the X. strumarium complex.