Purpose: Malignant pleural mesothelioma (MPM) is a rare and aggressive malignancy with poor prognosis. Patients with MPM who do not respond to standard first-line chemotherapy have limited treatment options. We evaluated the efficacy and safety of nivolumab, an immune checkpoint inhibitor, for the treatment of advanced or metastatic MPM. Patients and Methods: Japanese patients with unresectable, advanced, or metastatic MPM resistant or intolerant to ≤2 regimens of chemotherapy and ≥1 measurable lesion(s) were enrolled. Patients received nivolumab 240 mg intravenously every 2 weeks until progressive disease or unacceptable toxicity. The primary endpoint was objective response rate by central assessment according to the Modified Response Evaluation Criteria in Solid Tumors. Adverse events (AEs) and treatment-related AEs (TRAEs) were evaluated. Results: Thirty-four patients were enrolled between July 2016 and October 2016. Median follow-up was 16.8 (range: 1.8–20.2) months. Ten (29%, 95% confidence interval, 16.8–46.2) patients showed a centrally assessed objective response. The objective response rates were 26% (7/27), 67% (2/3), and 25% (1/4) patients for epithelioid, sarcomatoid, and biphasic histologic subtypes, respectively. Median duration of response was 11.1 months with a 68% disease control rate. Median overall survival and progression-free survival were 17.3 and 6.1 months, respectively. The objective response rate was 40% with programmed death-ligand 1 expression ≥1% and 8% with <1%. Thirty-two patients (94%) experienced AEs and 26 (76%) experienced TRAEs. Conclusions: Nivolumab met the primary endpoint as second- or third-line treatment for patients with MPM and showed promising efficacy with manageable toxicity. See related commentary by Mansfield and Zauderer, p. 5438