Abstract: Objective To evaluate the ffcacy of serum exosomal miR-125b, miR-21, miR- 122 and miR-375 in the diagnosis of hepatocellular carcinoma ( HCC)，and predict the potential target genes regulated by miR-125b. Methods The clinical data of 46 HCC patients, 11 patients with chronic hepatitis B virus ( CHB) and 50 healthy controls, including age, gender, serum alpha fetoprotein ( AFP), 0- L-fucosidase ( AFU) and other indicators，were collected. The exosomes in their serum samples were isolated, purified and identified, and the expression levels of exosomal miR-125b, miR-21, miR-122 and miR -375 were detected by real-time fluorescence quantitative polymerase chain reaction ( RT-qPCR ). The efficacies of individual and combined indicators for the diagnosis of HCC were evaluated by the ROC curve. The potential target genes of miR-125b were predicted by the miRTarBase. V8, TarBase. V8 and miRecords databases. The signal transduction pathways involved in miR- 125b were inferred by the analysis of clusterProfiler software. Results The extracted and purified serum samples contained a large number of exosome particles. The results of RT-qPCR showed that the expression levels of miR-125b, miR-21 and miR-122 in HCC patients were significantly higher than those in CHB patients and healthy controls ( P<0.05). The results of ROC curve analysis showed that the AUCHC values of miR-125b, miR-21, miR-122, miR-375 , AFP and AFU for the screening of HCC were 0.900, 0.857, 0.827, 0.597, 0.881 and 0.733, respectively. However, the AUCROC values of combined detection of miR -125b+AFP，miR-125b+miR-21 and miR -125b+ miR-21 + AFP for the diagnosis of HCC could increase to 0.927, 0.919 and 0.941, respectively. Nine target genes potentially regulated by miR- 125b，including TP53INPI, BAKI ,CEBPG, E2F3, ERBB2, ERBB3, NTRK3, SMO and SGPLI，were predicted by the database. The analysis of clusterProfiler software suggested that miR- 125b might directly or indirectly be involved in the p53 signalling pathway, miRNAs in cancer, cell aging, transforming growth factor (TGF)-β sigalling pathway, and etc. Conclusion The expression levels of miR-125b, miR-21 and miR-122 in serum exosomes of patients with HCC are increased, and their combination with AFP can improve the diagnostic efficiency of HCC, which may become the candidate markers for the diagnosis of HCC.