Host anti-tumor immune responses can be attenuated by suppressor T cells of the phenotype CD8⁺CD28⁻ (T_s cells). In the present study, we investigated the presence of CD8⁺CD28⁻ (T_s cells) in the peripheral blood compartment of gastric cancer (GC) patients. Flow cytometry was used to detect the population of CD8⁺CD28⁻ T_s cells present in peripheral blood in therapy naïve patients with gastric cancer (n = 26), postoperative chemotherapy naïve gastric cancer patients (n = 23), and healthy controls (n = 27). Meanwhile, the clinical data of gastric cancer patients were analyzed. A significant difference in the percentage of T_s cells was observed when comparing peripheral blood samples from cancer patients to healthy volunteers (27.08 ± 1.60% versus 10.86 ± 0.75%). In the patient group, the percentage of CD8⁺CD28⁻ cells among lymphocytes was higher in patients with LN metastasis than those without LN metastasis. The percentage of CD8⁺CD28⁻ cells was also related to tumor infiltration and size, but not with the degree of differentiation of cancer cells. Moreover, the percentage of CD8⁺CD28⁻ cells was higher in preoperative gastric cancer patients (26.24 ± 1.78%) than in those of postoperation patients (15.79 ± 1.11%). These findings may reflect the possibility of tumor-induced immunosuppression, and they should be complemented with further studies.