INTRODUCTION: We hypothesized that ramucirumab could increase previously reported objective response rate (ORR) of 11% of single-agent nivolumab in the second-line therapy of unresectable mesothelioma. METHODS: This was a cooperative group, single-arm, phase 2 trial enrolling patients with unresectable mesothelioma after progression on more than or equal to one pemetrexed-containing regimen. Ramucirumab and nivolumab were given intravenously every 14 days for up to 24 months. The primary end point was ORR; secondary end points were progression-free survival (PFS) rate at 24 weeks and overall survival (OS). RESULTS: Between April 2018 and October 2021, 34 patients were recruited. Median age was 72 (range: 40-89) years, 12% were women, and 79% of tumors had epithelial histology. Median follow-up was 10.2 months (interquartile range 19.6 mo [4.3-23.8]). ORR was 22.6% (95% confidence interval [CI]: 9.6%-41.1%) in all population and 43% (95% CI: 10%-82%) in patients with nonepithelioid histology. Of all patients, 45.2% (95% CI: 27.3%-64.0%) had stable disease. PFS rate at 24 weeks was 32% (95% CI: 17%-51%). Median PFS was 4.2 months (95% CI: 1.9-6.4 mo). Median OS was 12.5 months (95% CI: 6.3-23.5 mo). There was no grade greater than or equal to four toxicity. Programmed death-ligand 1 expression in the tumor did not correlate with benefit from treatment. Activation of tumor-infiltrating lymphocytes in response to treatment was associated with a trend toward improvement in PFS. CONCLUSIONS: Nivolumab and ramucirumab combination was safe and generated PFS and OS rates and ORR that compare favorably with single-agent nivolumab in a similar patient population. The primary end point of 40% ORR was not reached. Further investigation of this regimen in mesothelioma with nonepithelioid histology may be warranted. Clinical Trial Information: NCT03502746.