Background: We conducted a prospective observational study, DELIVER trial (UMIN000030850), to evaluate the real-world effectiveness of nivolumab monotherapy in previously treated advanced gastric cancer (GC) and have reported comparable efficacy and safety data (Takahashi, et al. Gastric Cancer 2021). There are few evidence regarding the association between tumor response and survival time in later-line treatment with nivolumab alone for advanced GC. We therefore report results from post-hoc exploratory analyses of survival time by tumor response from the DELIVER trial. Methods: The DELIVER trial enrolled 501 patients (pts) with advanced gastric or GEJ adenocarcinoma treated with nivolumab alone. Primary endpoint was overall survival (OS), secondary endpoints were response rate (RR), disease control rate, progression-free survival (PFS), tumor regression rate / tumor progression rate at 1st evaluation, tumor growth rate, and safety. The exploratory analyses were performed for survival according to tumor response and depth of response (DpR) in pts with measurable lesions who were receiving nivolumab as 3rd or later-line treatment. The survival data was fixed at the timepoint of 2 years after the last enrollment. Results: 234 pts were evaluable (median age 70y [26-90], 79% male, ECOG PS0/1/2 46/43/11%, 32% pts with ascites). Median OS was 6.5 months (95%CI 5.3-8.2) and median PFS was 1.8 months (95%CI 1.6-2.0). The RR was 15.0% (95%CI 10.4-19.5) with 5 complete response (CR) and 30 partial response (PR). The median PFS and OS were not reached for pts with CR, 11.7 and 29.8 months for pts with PR, 3.8 and 11.4 months for pts with stable disease, and 1.5 and 4.2 months for pts with progressive disease, respectively. In addition, the median DpR was -14.1% and was associated with PFS and OS in the Spearman analysis (r=0.55 and r=0.44, respectively). When the DpR was divided into 5 groups according to tumor shrinkage, there was difference in PFS and OS. Conclusions: This exploratory analysis indicated the association between DpR and survival time in pts with advanced GC treated with nivolumab alone in later-line. Increasing DpR was associated with longer median PFS and OS. Clinical trial information: UMIN000030850.