〔Abstract〕 Objective To establish an enzyme-linked immunosorbent assay(ELISA) for exosome B7-H3 in plasma, and to explore the clinical significance and diagnostic value of exosome B7-H3 in plasma from non-small cell lung cancer(NSCLC). Methods The plasma of 70 NSCLC patients(NSCLC group) and 36 healthy controls(HC group) were collected. Exosomes and microvesicles in plasma were separated by ultra-fast centrifuge method, and the expression levels of B7-H3 in plasma exosomes in NSCLC groups and HC groups were compared by Western blot method. In NSCLC group, the expression levels of B7-H3 in plasma exosomes and microvesicles in NSCLC group were compared. A simple and feasible ELISA method was established to detect the expression level of exosome B7-H3 in plasma by means of polyethylene glycol(PEG) precipitation and its clinical significance was analyzed. Logistic regression model was established to predict plasma-derived exosome B7-H3 as a risk factor, and receiver operating characteristic curve(ROC) was used to investigate the diagnostic value of exosome B7-H3 in NSCLC. Results For exosomes and microvesicles in plasma which were extracted by ultracentrifugation, Western blot results showed that the expression level of B7-H3 in plasma exosomes of NSCLC group was higher than that of HC group(P=0.032), and the expression level of B7-H3 in plasma exosomes was higher than that of microvesicles of NSCLC group(P=0.012). The expression level of exosome B7-H3 in plasma extracted by PEG precipitation was also higher in NSCLC group than that in HC group(P=0.024). The expression level of exosome B7-H3 in plasma of NSCLC patients was not related to gender, age, smoking or pathological type, but was related to T stage(P=0.002), N stage(P