Some retrospective studies in different populations have evaluated the prognostic value of microsatellite instability status (MSI) in patients with gastric cancer (GC). A small number of studies have focused on the effect of MSI status on the outcome of GC patients who have received adjuvant chemotherapy (CT). Medical records of 318 patients with stage II or III GC who had been treated with adjuvant CT after D2 gastrectomy between 2016 and 2019 were scanned. Eligible patients were divided into two groups: MSI-H and microsatellite stable (MSS). The determinant factors were examined using Cox regression analysis. A statistical significance level of alpha was accepted as p < 0.05. The study included 207 GC patients and 21 (10.1%) MS-high patients. A median disease-free survival was not reached (95% CI NR) in MSI-H patients, whereas a median disease-free survival was 30 months in MSS patients (95% CI 24.3-35.6) (p= 0.046). A median overall survival (OS) was not reached in MSI-H patients, whereas a median overall survival of 46 months (95% CI: 28.8 - 60.1) was reached in MSS patients (p= 0.032). In the multivariate Cox regression analysis for OS, female gender and MSI-H status were positive predictors of OS, whereas stage III disease negatively affected OS (p= 0.009, p= 0.030, and p= 0.009, respectively). Microsatellite instability status may be a prognostic factor in stage II and III Turkish GC patients who have received adjuvant oxaliplatin-based CT.