Abstract: In this paper,chlorination of commercial humicial acids was used as an experin ental model The single cell gel elec trophoresis assay was used to detect DNA dan age and reprir educed by chlorinated hum icacids in V79 cells The results revealed that the chlorinatedhuln icacids could induce DNA danage of V79 cells and the breakage could be repaired within two hours inclubation The study suggested that the use of commercial humic acid as a model substrate w as apprepriate for exan fining the formation of mutagenic cheanicals during Water treatment.