Background: Recently, the proportion of elderly patients (pts) with metastatic gastric cancer (mGC) has increased in Japan. Survival benefits of salvage treatment after second-line chemotherapy (CTX) for mGC were shown in several prospective studies. However, the role of salvage treatment in elderly pts remains controversial. Methods: We reviewed 185 pts with mGC who received palliative CTX aged ≥ 70 years at our institution between April 2007 and March 2018. Eligibility criteria were as follows: PS 0-2, refractory to first-line and second-line CTX. The purpose of this study was to evaluate the clinicopathologic factors that affected overall survival for elderly pts with mGC, univariate and multivariate analyses were performed on the baseline factors at the beginning of third-line CTX. Results: Of all, 71 pts were eligible. Median age was 75 years (71-85). Median progression-free survival (PFS) and overall survival (OS) for third-line CTX were 3.2 and 7.5 months, respectively and an overall response rate and disease control rate were 4.2% and 43.7%, respectively. In univariate analysis, the following four factors were identified to have prognostic significance: performance status (PS) (ECOG 0–1 or 2), serum albumin level (< 3.5 or ≥ 3.5 g/dl), serum LDH level (≤ 240 or > 240 IU/l), PFS under second-line CTX (< 3 or ≥ 3 months). Multivariate analysis found three prognostic factors affecting poor survival following third-line CTX: PS of 2 (hazard ratio (HR) 8.89, 95% confidence interval (CI) 3.99–20.2; P = 0.001), serum LDH level > 240 IU/l (HR 2.75, 95% CI 1.48–5.05; P = 0.002) and median PFS under second-line CTX of < 3 months (HR 1.89, 95% CI 1.01–3.43; P = 0.045). A prognostic index was constructed, dividing pts into low- (0 factor), intermediate- (1-2 risk factors), or high- (3 risk factors) risk groups. Median OS for each group were 12.6, 6.0 and 3.0 months, respectively (P< 0.001). Conclusions: This analysis suggests that some clinicopathologic factors might be helpful in identifying the subgroup of elderly pts most likely to benefit from third-line CTX for metastatic gastric cancer.