The comet assay(the alkaline single cell gel electrophoresis) was applied universally in the field of ecotoxicology as a sensitive bioassay to detect DNA damage in the cell level.Little has been reported on its application in assessing effects of mutagens on earthworms in the soil ecosystem.In this paper,earthworms(Eisenia f oetida) were exposed to different levels of mitomycin C and soil samples collected from an area irrigated with wastewater for years.After the exposure,coelomecytes of the earthworms were extracted and subjected to comet assay.The samples were compared in endpoints,such as tail length(TL),tail DNA content(TD) and tail moment(TM).Results show that the utilization of comet assay in combination with vivo exposure of earthworms is a promising tool for evaluation of mutagenic chemicals and polluted soil,and that among the endpoints,TM and TL are more sensitive in representing the dose-effect relationship.