Gastric cancer is one of the most common malignant tumors in clinical practice, and has a high incidence rate and high mortality rate. In recent years, a great progress has been made in the immunotherapy of gastric cancer with immune checkpoint inhibitors (ICIs). However, the overall effective rate of monotherapy is still low, and it is often accompanied by different degrees of immune related adverse reactions. Therefore, it is urgent to find accurate and reliable biomarkers to screen patients with potential benefits from immunotherapy. Tumor mutation burden (TMB), which is characterized by the number of tumor gene mutations, has shown a correlation with the efficacy of ICIs. Here, the authors review the associations of TMB with the clinicopathologic characteristics of gastric cancer, and the prediction of immunotherapy efficacy as well as other biomarkers.