〔Abstract〕 To establish an enzyme-linked immunosorbent assay (ELISA) for exosome B7-H3 in plas- ma , 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 . Lo- gistic regression model was established to predict plasma-derived exosome B7-H3 as a risk factor , and receiver op- erating characteristic curve (ROC) was used to investigate the diagnostic value of exosome B7-H3 in NSCLC . Re- sults 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 < 0. 001) , M stage (P = 0. 010) and AJCC stage (P < 0. 001) . Multivariate Logistic regres- sion analysis identified exosome B7-H3 in plasma as a risk factor for NSCLC . ROC analysis showed that the sensi- tivity of exosome B7-H3 in plasma for the diagnosis of NSCLC (0. 843) was higher than that of carcinoembryonic antigen (CEA) (0. 743) , whereas the specificity (0. 722) was lower than that of CEA (0. 833) . Combined de- tection of exosome B7-H3 and CEA (AUC = 0. 928 , 95% CI:0. 877 - 0. 979) had a higher diagnostic performance for NSCLC . Conclusion B7-H3 in plasma exosomes is related to the cancer staging of NSCLC , and the combined detection of exosome B7-H3 and CEA in plasma is conducive to the laboratory diagnosis of NSCLC .