Background <p>Systemic chemotherapy may relieve symptoms and induce tumor downstaging in patients with unresectable gastric cancer. However, the survival benefit of primary tumor resection after chemotherapy remains unclear. This study aimed to determine the survival outcomes of conversion surgery in patients with unresectable gastric cancer.</p> Methods <p>This retrospective cohort study reviewed the data of patients with unresectable advanced gastric cancer treated with systemic chemotherapy between 2005 and 2019. The primary outcome was overall survival (OS). Patient characteristics and clinicopathological stages were assessed. The rates of conversion surgery and tumor progression after conversion surgery were determined.</p> Results <p>The study included 86 patients, of whom 26 (30.2%) responded to systemic chemotherapy and underwent conversion surgery. Most patients had a diffuse-type, poorly differentiated adenocarcinoma, a single non-curative factor, and peritoneal metastasis, if present. The leucovorin plus oxaliplatin regimen was the dominant first-line chemotherapy regimen. All patients who underwent conversion surgery achieved R0 resection. The median time to progression was 8.9 months. The median survival time was 25.8 (95% confidence interval [CI], 19.88–32.85) months in the conversion group and 10.1 (95% CI, 6.54–11.93) months in the non-conversion group (<i>p</i> &lt; 0.001).</p> Conclusions <p>For patients with unresectable advanced gastric cancer who respond favorably to systemic chemotherapy, conversion surgery should be considered as a treatment option. This approach can improve OS and delay disease progression. Nonetheless, the present study could not reveal the predictors of OS besides chemotherapy resistance. Therefore, a multimodal approach combining systemic chemotherapy with conversion surgery should be considered.</p>