It has been an established fact that exosomes act as a mediator in tumor microenvironment as well as participate actively in intercellular communication between cancer cells. Exosomes carry a variety of molecular cargoes that prevent cyclic degradation and represent the cells of their origin. In this study, the difference in expression levels of exosomes was measured for diagnosis of gastric cancer. We isolated exosomes from plasma by size-selective method. The morphology of the exosomes was characterized by transmission electron microscopy, and the particle size and concentration of the exosomes were detected by NanoSight's Nanoparticle Tracking Analysis. Results indicated that the expression level of exosomes in gastric cancer patients was higher than that in healthy individuals. The specificity and sensitivity were 65.2% and 73.1%, respectively. Currently, clinical tumor markers for gastric cancer detection mainly included Carbohydrate antigen 72-4 (CA72-4), Alpha-fetoprotein, Carbohydrate antigen 125, Carbohydrate antigen 19-9 (CA19-9), Carcinoembryonic Antigen, Carbohydrate antigen 242. When we combined positive rate for combined gastric cancer biomarkers, results showed that exosomes concentration +CA19-9 and exosomes concentration +CA72-4 in the two-combined test can provide enough positive rate. Therefore, it can be concluded that for gastric cancer, the concentration of exosomes may be regarded as a diagnostic indicator, eventually.