The sensitivity to dimethomorph of 125 Phytophthora capsici strains collected from Hebei, Mongolia, Shannxi, Anhui and Beijing were determined by mycelia growth inhibition method. The results showed that EC₅₀ values ranged from 0.126-0.318 μg/mL. EC₅₀ of the most insensitive strains was 2.5 folds of the most sensitive ones with a mean of 0.218±0.0368 μg/mL. The sensitivity frequency of P. capsici to dimetho-morph distributed as a unimodel curve, which showed there was no resistant subpopulation among these isolates, so this sensitivity baseline was suitable for resistance monitoring of P. capsici to dimethomorph. 12 resistant mutants to dimethomorph were obtained from N-7 parental strain in vitro by UV-irradiating, and the resistant factors ranged from 16.38-132.15 folds. One very high resistant mutant with 680 folds resistance factor was also selected from DZ-16 strain. The parental strains and their mutants were investigated for mating type. Some biological characteristics of mutants were studied in laboratory. The results indicated that the mutants possessed consistant pathogenicity with their parental strains. As compared to their original strain, sporulation ability of resistant mutants were increased in vivo, the quantity of asexual spores corresponded to that of sensitive strains in vitro and the resistant mutants exhibited diversity in mycelial growth rate. All the strains were A1 mating type. Based on the above, the resistant mutants would favor the development of dimethomorph-resistant population. It was suggested that the dimethomorph should be used alternately with other no cross-resistant fungicides to avoid or delay the development of resistance.