The aim of this study was to determine optimal therapeutic dose of antifungal agents for dermatophytes. Forty nine dermatophytes were isolated form dogs and cats showing skin lesions and were tested for their in vitro susceptibility to nystatin, griseofulvin, terbinafine, ketoconazole and fluconazole by broth microdilution test. Terbinafine showed the lowest MIC value among the antifungal agents tested, and MIC values ranged from 0.002 to 0.016 $mu extrm{g}$/ml. Fluconazole showed the highest MIC values among the antifungal agents tested, and MIC values ranged from 32 to 512 $mu extrm{g}$/ml. MIC values of nystatin, griseofulvin and ketoconazole ranged from 1.12 to 4.48 $mu extrm{g}$/ml, 0.5 to 4.0 $mu extrm{g}$/ml, and 1.6 to 12.8 $mu extrm{g}$/ml, resistant to griseofulvin, and that antifungal susceptibility test was needed to determine optimal therapeutic dose of antifungal agents for each dermatophyte.