Background: Nivolumab has changed the treatment of advanced gastric cancer (AGC). Nivolumab shows better outcomes compared to best supportive care among AGC patients who received at least two prior regimens. However, there are no reliable data regarding AGC patients with poor performance status (PS) who received nivolumab. We investigated the efficacy and safety of nivolumab among AGC patients with poor PS. Methods: We retrospectively collected clinicopathologic data from patients with AGC who underwent nivolumab monotherapy at our institution from October 2017 to June 2019. Results: Forty-nine AGC patients who received nivolumab were assessed. Twenty-seven patients had PS 0 or 1 (Good group) and 22 had PS 2 or 3 (Poor group). The median progression-free survival and overall survival durations were 2.0 and 6.0 months in the Good group, respectively, and 1.2 and 2.8 months in the Poor group, respectively. The overall survival was significantly shorter in the Poor group (6.0 vs 2.8 months, p = 0.0255). The disease control rates were 23 and 9% in the Good and Poor groups, respectively. Thirty-three percent of patients experienced immune-related adverse events in the Good group, and 18% in the Poor group. Conclusion: Nivolumab is feasible but insufficient as third-or later-line treatment for AGC patients with poor PS.