An 85-year-old female was admitted to our hospital for left ureteral cancer and para-aortic lymph node metastasis. To control hematuria, a laparoscopic retroperitoneal nephroureterectomy was performed, and papillary urothelial carcinoma (pT3b) was found. To treat para-aortic lymph node metastasis, she received chemotherapy with gemcitabine and nedaplatin. After 2 cycles, a computed tomography scan revealed its disappearance; however, bilateral lung metastases appeared. The patient was administered second-line therapy with pembrolizumab every 3 weeks. After 3 courses, lung metastases disappeared and she achieved a complete response. After the fifth administration of pembrolizumab, she was readmitted with right upper limb pain and weakness in both lower extremities. She was diagnosed with pembrolizumab-induced grade 3 peripheral neuropathy with Guillain-Barré syndrome-like onset. High-dose monocorticotherapy was initiated for treatment. Three weeks later, the pain and weakness of the limbs improved. After discharge, the dose of prednisolone was tapered and there was no relapse of adverse events. Pembrolizumab was discontinued at the onset of neuropathy, but she maintained a complete response.