Objective To detect the genotoxicity of Coreopsis tinctoria Nutt.（water extract） and provide research data for its safety evaluation.Methods The water extract of Coreopsis tinctoria Nutt. was used as the test substance in bacterial reverse mutation test， mouse lymphoma Assay （MLA） with and without metabolic activation S9； and the powder of Coreopsis tinctoria Nutt. was used in micronucleus test. Ames test based on the plate incorporation method was performed to detect his^-/trp^- revert mutation capabilities of S．typhimurium TA98， TA100， TA1535， TA1537 and E．coli WP2 uvrA induced under four doses of 1.25， 2.5， 5 and 10 mg/ plate； MLA based on the microporous method was performed to detect the increase of tk^-+/- mutation frequency （MF） of L5178Y cells induced by 5 concentrations of 1.5， 2.0， 2.5， 3.0 and 3.5 mg/mL under the treatment condition of ±S9/3 h， and to evaluate the damage effects on the tested cells； for the mouse bone marrow micronucleus test： CD-1 mice were administrated with 900 mg/kg， 1 800 mg/kg and 3 600 mg/kg of the Coreopsis tinctoria Nutt. powder （200 mesh） intragastrically for three times at an interval of 24 h， and the samples were collected by 18-24 h after the last dose. The micronucleated cells in 2 000 polychromatic erythrocytes were counted， and the micronucleated cell rate were calculated.Results Under both conditions absent and present S9， the numbers of the revertants in five strains induced by 1.25~10 mg/dish （equivalent to crude drug： 8.33~66.67 mg/plate） were not significantly increased compared with the negative （solvent） control of sterilized water for injection. The MF induced by 1.5~3.5 mg/mL （equivalent to crude drug： 10~23.33 mg/mL） were significantly increased with a concentration-response relationship， and most of the mutants were in the form of small colony. The T-MF and S-MF induced by 3.0 and 3.5 mg/mL +S9 groups were more than 3 times of the negative control group： the mean micronucleus rates in 900 mg/kg， 1 800 mg/kg and 3 600 mg/kg groups were 0.85±0.58， 1.10±0.97 and 1.45±1.12， respectively， with no significant difference compared with the deionized water negative control group.Conclusion The water extract of Coreopsis tinctoria Nutt. could significantly increase the mutation frequency of tk^+/- gene and led to chromosome damage in L5178Y cells， no matter with or without metabolic activation， suggesting its potential genotoxicity to human.