Abstract: The sensitivity and resistance risk of Phytophthora capsici to mandipropamid were studied.The sensitivity of 173 P.capsici strains to mandipropamid was determined by mycelia growth inhibition method.The results demonstrated that EC50 values ranged from 0.002 7 μ g/mL to 0.049 9 μ g/mL,with a mean value of 0.021 9±0.010 2 μ g/mL.The sensitivity frequency of P.capsici to mandipropamid distributed as a single peak curve.The 10 strains were separately treated by UV- irradiating with colony point change and taming,with 7 and 1 resistant mutants to mandipropamid separately obtained in vitro by UV-irradiating and taming,the resistant levels ranged from 41.50 to 394 437.77 times.Mutation frequencies were 1.46% and 1.43%,respectively.Some biological characteristics of mutants were studied in laboratory.The mutants exhibited diversity in mycelial growth rate,pathogenicity,sporulation ability,fitness and competition ability with their parental strains.The sporulation,fitness and competition of DX 2-3 20m and DX 2-3 F7 were higher than the parental strains,contributing to the formation of resistance strains.It was suggested that P.capsici had a moderate resistance risk to mandipropamid.