Among benign proliferation of the urinary bladder, polypoid cystitis is a rare disease in dogs. It is characterized by epithelial proliferation, chronic inflammation in lamina propria, and development of a polypoid mass or masses without evidence of neoplasia. This report describes histopathologic features of polypoid cystitis in dog. A 10-year-old spayed female shihtzu-dog was presented with two-month history of hematuria. Abdominal ultrasonography confirmed the thickened bladder wall and calculi in both kidneys. Surgical biopsy sample was taken from the thickeded bladder mucosa for the histopathologic examination. The mass was covered with irregular hyperplastic transitional epithelium with the projection into the lumen in multifocal areas as well as many Brunn's nests in lamina propria. Many inflammatory cells such as lymphocyte, plasma cell, and macrophage and few neutrophils were occupied in lamina propria and submucosa. Proliferated fibrous tissues in lamina propria were clarified by using special staining methods. These collagens were stained blue with Masson's trichrome and red with van Gieson, but negative for alcian blue. Based on the clinical, gross, and histopathologic examinations, this case was diagnosed as polypoid cystitis in a dog. In our best knowledge, this is first report of polypoid cystitis in dog in Korea.