Pembrolizumab was approved as second-line treatment for patients with metastatic urothelial cancer (UC) in Japan. We performed a retrospective pilot study to assess the potency of pembrolizumab treatment in Japan.The medical records of 40 consecutive Japanese patients with metastatic UC who started pembrolizumab between January and October 2018 were reviewed and statistically analyzed to clarify the efficacy and safety of the drug.The objective response rate, median progression-free survival period, and median overall survival period were 20.6%, 4.1 months and 10.0 months, respectively. Multivariate analysis indicated the presence of liver metastasis, worse performance status (≥2), and higher C-reactive protein as factors predictive of shorter OS.We demonstrated for the first time, a comparable efficacy and safety profile of pembrolizumab for Japanese patients with metastatic UC, as in the KEYNOTE-045 study. The results indicate the features of pembrolizumab therapy in the current Japanese clinical practice.