Several fungi may cause inflammatory reaction in the external auditory canal. Otomycosis is often chronic of recurrent and it may cause patient to complain of itching. Also it could result in excessive cerumen accumulation and a sense of blockage of the canal thereby impairing the hearing acuity. And it may be involved in an inflammatory process, invading the epithelium of the canal or drum head and causing acute symptoms. Although numerous drugs are available for the treatment of fungal infection of the external auditory canal, the mycological and clinical effects of most of such drugs are not satisfactory. In the hope of findings an effective durg for otomycosis, the authors observed fungistatic effects of 5-fluorocytosine. The results were as following ; 1) Out of 70 suspected otomycosis, 58 (82.8%) were confirmed from which 96 strains were isolated. 2) The identification of fungal flora were as follows ; Aspergillus sp. 73 strains, Penicillium sp. 11 strains, Mucor sp. 3 strains, Fusidium sp. 1 strain, Cladosporium sp. 1 strain, Unidentified 7 strains. 3) Among the Aspergillus, 31 strains of A. fumigatus, 20 strains of A. terreus, 5 strains of A. niger, 4 strains of A. flavus were identified. 4) The growth of most Aspergillus were inhibited by 5-fluorocytosine in low concentration of 0.1μg/ml to 1.6μg/ml. 5) The clinical symptoms disappeared within 5 days after treatment with 5-fluorocytosine in 57 cases (81.4%), with in 10 days in 11 cases (15.7%), but 2 cases (2.9%) showed persistent symptoms. 6) Significant inhibition of growth of fungi were noted within 6 days after treatment with 5-fluorocytosine in 49 cases (70.0%), within 12 days in 18 cases (25.7%) and 3 cases (4.3%) showed only slight inhibition.