Abstract: To assess the resistance risk of Botrytis cinerea to fludioxonil,the method for fludioxonil resistance mutagenesis and the biological characteristics of resistant mutants were studied.The results showed that the sub-lethal UV irradiation time for the conidia of B. cinerea was 90-120 seconds.Four wild sensitive parental isolates were irradiated for sub-lethal time by UV,and six resistant mutants were obtained from two parental isolates.The ratio of EC50 value of resistant mutants comparing with that of its parental strain was more than 310 times,the frequency of resistance mutation was 3.13×10-7.The mycelial growth rate,sporulation,sclerotia production and pathogenicity of resistant mutants decreased significantly as compared with their parental isolates.The analysis showed that the mutants had no cross resistance to other fungicides that have different mechanisms.The above results indicated that B. cinerea on tomato had low risk of resistance to fludioxonil.