Cytological, histopathological and immunohistochemical examinations were carried out on a presumed 10-year-old Japanese cat showing vomiting and emaciation. On cytologic examination of the mass of the upper abdominal cavity, many yeast-like organisms were detected in the macrophages. At necropsy, the upper part of colon was markedly dilated with a thickened wall. The lung did not show significant changes. Histologically, severe necrotic and granulomatous lesions were observed in the colon. In the colonic lesion, the cytoplasm of the macrophages contained yeast-like organisms with irregularly shaped dots, and the cell walls of these organisms were stained black by Grocott-Gomori methenamine-silver stain. Immunohistochemically, they were found to be positive for anti-histoplasma yeast antibody. This is the first report of feline histoplasmosis in Japan.