A recurrence of hepatocellular carcinoma (HCC) after living donor liver transplantation (LDLT) is one of the major concerns reflecting the higher mortality of HCC. This study aimed to explore the impact of circulating exosomes on HCC development and recurrence. One‐shot transfusion of hepatoma serum to naïve rats induced liver cancer development with gradual elevation of alpha‐fetoprotein (AFP), but exosome‐free hepatoma serum failed to induce AFP elevation. The microarray analysis revealed miR‐92b as one of the highly expressing microribonucleic acids in hepatoma serum exosomes. Overexpression of miR‐92b enhanced the migration ability of liver cancer cell lines with active release of exosomal miR‐92b. The hepatoma‐derived exosomal miR‐92b transferred to natural killer (NK) cells, resulting in the downregulation of CD69 and NK cell‐mediated cytotoxicity. Furthermore, higher expression of miR‐92b in serum exosomes was confirmed in HCC patients before LDLT, and its value at 1 month after LDLT was maintained at a higher level in the patients with posttransplant HCC recurrence. In summary, we demonstrated the impact of circulating exosomes on liver cancer development, partly through the suppression of CD69 on NK cells by hepatoma‐derived exosomal miR‐92b. The value of circulating exosomal miR‐92b may predict the risk of posttransplant HCC recurrence. This study demonstrates the impact of circulating exosomes on liver cancer development in rats, explores functional roles of exosomal miR‐92b in the tumor microenvironment, and verifies its clinical value for early prediction of posttransplant hepatocellular carcinoma recurrence.