Introduction The outcomes of robotic gastrectomy (RG) for gastric cancer remain unclear due to a lack of prospective studies. We had previously designed and conducted a prospective phase II study of RG that showed favorable short-term outcomes. Herein, we aimed to determine the long-term outcomes of RG for clinical stage I gastric cancer. Patients and methods This single-center, prospective phase II study enrolled patients with clinical stage I gastric cancer undergoing RG. The survival outcomes, which were the secondary endpoints of the study, were evaluated. Results Between December 2012 and April 2015, 120 patients were enrolled in this study. The 5-year overall survival (OS) was 96.7% (95% confidence interval CI 91.5–98.7%). The 5-year recurrence-free (RFS) and disease-specific survival (DSS) rates were 96.7% (95% CI 91.5–98.7%) and 99.2% (95% CI 94.3–99.9%), respectively. When confining the analysis to distal and pylorus-preserving gastrectomy, the 5-year OS, RFS, and DSS were 98.1% (95% CI 92.7–99.5%), 98.1% (95% CI 92.7–99.5%), and 100%, respectively. Only one patient died due to relapse of gastric cancer, while three died from other causes. Conclusions Long-term outcomes of RG was comparable to those of open and laparoscopic gastrectomy when the surgeries were performed by experienced surgeons in a high-volume center.