Immune checkpoint inhibitors (ICIs) provide excellent benefits to the treatment of various cancer types, including urothelial carcinoma. Conversely, they can cause immune-related adverse events (irAEs), and some of them are severe or fatal. Furthermore, evidence on the safety and effectiveness of the readministration of ICIs after the occurrence of irAEs is limited. In this case report, a 78-year-old man who suffered from metastatic right renal pelvic cancer was treated with pembrolizumab. He had a partial response to pembrolizumab, but he developed grade 3 myasthenia gravis. The myasthenia gravis symptoms were immediately relieved by corticosteroids and intravenous immunoglobulin therapy. When the disease rapidly progressed, he was treated again with pembrolizumab. After 5 days, a chest radiograph showed shrinkage of pulmonary metastases. Unfortunately, he died of multiple brain infarctions 7 days after the readministration. We report this case with a literature review on the efficacy and safety of the readministration of ICIs after the occurrence irAEs including myasthenia gravis.