Background: KSCC1701 trial showed the efficacy and safety of S-1 plus ramucirumab as a first-line treatment for elderly patients with advanced/recurrent gastric cancer. However, some frail patients may not benefit from S-1 plus ramucirumab. We aimed to clarify the usefulness of G8 screening tool for stratifying the efficacy and safety of S-1 plus ramucirumab therapy to elderly patients with advanced/recurrent gastric cancer. Methods: Patients aged 70 and older with previously untreated unresectable or recurrent gastric cancer were included from 23 institutes in Japan. They received S-1 (40-60 mg twice daily for 28 days, every 6 weeks) plus ramucirumab (8 mg/kg, every 2 weeks) until disease progression. The primary endpoint was the one-year survival rate. The secondary endpoints included progression-free survival (PFS), overall survival (OS), response rate (RR), and safety. The exploratory endpoint was detection of differences in treatment response by G8 screening tool. Results: Between September 2017 and November 2019, 48 patients were enrolled in this study. The cut-off value of G8 was determined as 11 by time-dependent ROC curve analysis for OS. Patients of G8 high (> = 11) and low (< 11) were 31 and 15, respectively. The characteristics of patients with G8 high/low were male: 21 (65.6%)/13 (81.3%), median age: 77/78 years, and PS (0): 16 (50.0%)/4 (25.0%). The one-year survival rate (total/G8-high/G8-low) was 65.2%/82.6%/26.7%. The median OS and PFS (total/G8-high/G8-low) were 16.4/20.7/6.9 months and 5.8/7.2/3.9 months, respectively. On Cox proportional hazards regression analysis for OS and PFS, the hazard ratio of G8-high was 0.156 [95%CI:0.066-0.367 (p < 0.0001)] and 0.391 [95%CI:0.202-0.755 (p = 0.0038)], respectively. The best RR (total/G8-high/G8-low) was 41.9%/55.6%/23.1%. The frequent grade 3 adverse events (total/G8-high/G8-low) was 78.7%/77.4%/81.3%. The frequent grade 4 adverse events (total/G8-high/G8-low) was 14.9%/16.1%/12.5%. Conclusions: Based on the results, G8 screening tool is useful for selecting elderly patients with advanced/recurrent gastric cancer in whom S-1 plus ramucirumab treatment shows a longer survival and a higher RR. Further examination including adverse events is therefore warranted. Clinical trial information: UMIN000028309.