Objective To analyze the serum PD-L1 levels of gastric cancer patients and its relationship with tumor stage and prognosis.Methods Serum of sixty patients with pathological diagnosis of gastric cancer in our hospital from August 2018 to December 2019 were collected,and the serum of 15 healthy adults as a control.The serum PD-L1 levels was measured by enzyme linked immunosorbent assay(ELISA).The serum PD-L1 levels between gastric cancer patients and healthy adults were compared.The relationship between the serum PD-L1 levels and prognosis of gastric cancer patients with different stages was analyzed.Finally,the PD-L1 expression in tumor tissues was detected by immunohistochemical staining,and its correlation with serum PD-L1 levels was analyzed.Results The serum PD-L1 levels of gastric cancer group was significantly higher than that of the control group.The serum PD-L1 levels in patients with stage Ⅲ and Ⅳ gastric cancer was significantly higher than that in stage Ⅰ and Ⅱ.The serum PD-L1 levels in gastric cancer patients with peritoneal metastasis was significantly elevated,indicating poor prognosis.Kaplan-Meier survival analysis showed that the survival time of gastric cancer patients with higher level of serum PD-L1 was shorter than those with lower ones.We further evaluated the PD-L1 expression in tumor tissues.There was no significant correlation between the serum PD-L1 levels and that in tumor tissues.Conclusions The serum PD-L1 levels of gastric cancer patients was higher than that of healthy adults,and which gradually increased with the progression of the disease.Gastric cancer patients with peritoneal metastasis had a much higher serum PD-L1 levels,and there was no significant correlation between serum PD-L1 levels and PD-L1 expression in tumor tissues.