We previously reported that claspin is a key regulator in the progression of gastric cancer and renal cell carcinoma. However, the clinicopathological significance of claspin in urothelial carcinoma (UC) has not been investigated. We analyzed the expression and distribution of claspin in UC cases by immunohistochemistry. In the non-neoplastic urothelium, the expression of claspin was either weak or absent, whereas UC tissues showed nuclear staining. The expression of claspin was detected in 58 (42%) of a total of 138 upper tract UC cases treated by radical nephroureterectomy without neoadjuvant chemotherapy. Claspin-positive UC cases were associated with nodular/flat morphology, variant histology, high tumor grade, high pathological T grade, and lymphatic and venous invasion. The expression of claspin was significantly associated with decreased progression-free survival and cancer-specific survival. In addition, claspin was co-expressed with Ki-67, PD-L1, HER2, EGFR, and p53 in consecutive tumor sections of UC. An immunohistochemical analysis of claspin in biopsy specimens revealed that strong to moderate claspin staining was more frequently observed in carcinoma in situ in comparison to dysplasia or the benign urothelium. Furthermore, immunocytochemistry for claspin on urine cytology slides demonstrated that the proportion of claspin-positive cells was significantly greater in high-grade UC than in benign cases. These results suggest that claspin may be a novel prognostic marker and a possible therapeutic target molecule for UC. Moreover, claspin could be a useful diagnostic biomarker of urothelial neoplasia.