Eosinophilic cystitis (EC) is a rare inflammatory disorder in dogs. Although EC has been associated with various etiological factors, the precise cause of this disease remains unclear in human and animals. A 7-year-old female Yorkshire terrier was presented with 3-week-history of hematuria, dysuria, and suprapubic pain. A bladder mass in ventral surface and urinary calculi were noted on ultrasonography and gross findings. Biopsy sample was taken from the protruded mass of bladder for histopathologic examination. Hyperplastic transitional epithelium with focal ulceration covered the bladder mass. A large nodule of fibrous tissue that contained fibrocytes, fibroblasts, Iymphocytes, plasma cells, macrophages, numerous eosinophils, and abundant blood vessels was occupied in lamina propria and submucosa of bladder mass. Based on the clinical, gross, and histopathologic examinations, this case was diagnosed as EC in a dog. In our knowledge, this is the first report of an eosinophilic cystitis in dog in Korea.