We report a case of retroperitoneal fibrosis due to Schistosoma Japonicum in patient with urothelial carcinoma. Retroperitoneal fibrosis was observed in a-83-year-old man during examinations for postrenal renal failure. The symptoms were improved by percutaneous nephrostomy and pulse therapy using corticosteroids, however, urothelial carcinoma was detected during follow-up examinations. The biopsy of retroperitoneal tissue was performed during the surgery for urothelial carcinoma. The histopathological examination revealed scattered calcified eggs of Schistosoma Japonicum in retroperitoneal fibrosis tissue. Therefore, in this case, we assumed Schistosoma Japonicum was the cause of retroperitoneal fibrosis. In our knowledge, there is no report about retroperitoneal fibrosis due to Schistosoma Japonicum. We hypothesize the pathway that the eggs penetrate into retroperitoneal space is extravasation from intestinal wall and peritoneal cavity, although the detail of this mechanism is not obvious. It is well known about the relationship between Schistosomasis and malignant tumors. However, it seemed no evidence regarding the relationship between Schistosoma Japonicum and urothelial carcinoma, since there is no report about it and the eggs were not found in specimen of urothelial carcinoma.