A 72-year-old male was referred to us five months ago as his medical check had disclosed asymptomatic left pleural effusion. A contrast-enhanced chest computed tomography (CT) revealed multiple pleural nodules with pleural effusion in his left chest. A diagnosis of malignant pleural mesothelioma of epithelioid type, cT4N2M0 Stage IV was made by a biopsy of the left pleural nodule. After two courses of cisplatin and pemetrexed, the left pleural nodule enlarged, and he was treated by nivolumab two months after. At the end of three courses of treatment, the patient noted froth in his urine. Laboratory examination showed proteinuria and decrease of plasma albumin. There was a little proteinuria before nivolumab administration and the serum albumin level had been normal. A renal biopsy showed no glomerular cell proliferation, no membranous changes, and no semilunar formation but CD8 dominant lymphocyte infiltration in the tubular interstitium. We diagnosed him as a case of minimal change nephrotic syndrome after nivolumab treatment. No progress of the tumor was observed three months after discontinuation of nivolumab treatment. Nephrotic syndrome in this patient was considered an immune-related adverse effect (irAE). Nephrotic syndrome as an irAE is a rare complication of treatment with immune checkpoint inhibitors, especially nivolumab. It has been reported only once in the treatment of malignant melanoma.