Abstract: Peritoneal mesothelioma (PeM), which originates in cells in the visceral and mural layers of the peritoneum, is a rare and highly aggressive malignant tumor that accounts for approximately 15% of all mesotheliomas. The disease is characterized by insidious onset and poor prognosis, and its mechanisms of tumorigenesis and progression have not been fully elucidated. Asbestos exposure is a major risk factor for mesothelioma. Effective treatment options alternative to cytoreductive surgery (CRS), hyperthermic intraperitoneal chemotherapy (HIPEC), and platinum/pemetrexed (conventional treatments) are currently lacking. Immunotherapy, which mobilizes the immune system, has shown initial efficacy in patients with advanced mesotheliomas. However, additional real-world clinical trials and studies on immunotherapeutic targets remain needed. This article reviews progress in PeM-related immunotherapy clinical studies and potential targets in PeM treatment.