Mesothelioma is a rare and aggressive tumor originating from the serosal lining of the pleural, peritoneal and pericardial cavities. There are very few cases diagnosed with malignant peritoneal mesothelioma reported in childhood. Thanks to the developments in the field of immunotherapy, the prognosis of the disease has improved with the addition of the immune check point inhibitor, an anti-programmed death-1 monoclonal antibody, nivolumab to the treatment of MPM. In the treatment of our case who was diagnosed with diffuse malignant peritoneal mesothelioma at a very early age; cytoreductive surgery, hyperthermic intraperitoneal chemotherapy, platinum and pemetrexed combination chemotherapy and nivolumab were used. Our patient, who has been on nivolumab therapy for 14 months and has been followed up for 20 months since her diagnosis, is still in remission. This case supports the utility of nivolumab in pediatric MPM.