Background: Gastric cancer is the third cause of cancer-related deaths worldwide, and is initially detected and attacked by the immune system through tumor-reactive T cells. The aim of this study was to determine the basic characteristics of the peripheral blood T-cell receptor (TCR) repertoire in patients with gastric cancer. Methods: High throughput sequencing was used to identify hyper-variable rearrangements of complementarity determining region 3 (CDR3) of the TCR β chain to comprehensively profile the TCR repertoire in peripheral blood samples from 6 advanced gastric cancer patients and 3 early gastric cancer controls. Results: The study showed that the TCR repertoire differed substantially between advanced cancer patients and early controls in terms of CDR3 clonotype, diversity and V/J segment usage. Specifically, low diversity reflected a worse immune status and prognosis in advanced gastric cancer. However the diversity of TCR was not significant difference in wild or mutation patients. Conclusion: TCR repertoire analysis served as a useful indicator of disease development and prognosis in gastric cancer and may be utilized to be biomarker for immunotherapy.