Hepatitis B virus (HBV) has been reported to be recognized by dendritic cell-specific ICAM-3-grabbing nonintegrin in the presence of the -mannosidase I inhibitor kifunensine, whereas native HBV is not. The aim of our study was to determine whether changes in -mannosidase I expression in peripheral blood mononuclear cells (PBMCs) occur in patients with HBV infection. Peripheral blood was collected from 90 HBV-infected patients (grouped into immune tolerance, chronic hepatitis B, or inactive carrier group based on their clinical states) and 30 healthy donors. Expression of the three -mannosidase I subtypes, MAN1A1, MAN1A2, and MAN1C1, was measured using western blot analyses. Compared with the healthy controls, significant increases in the MAN1A1, MAN1A2, and MAN1C1 expression levels were observed in the three HBV-infected groups, among whom the immune tolerance group showed the largest increase. For the patients in the immune tolerance phase, the expression levels of both MAN1A1 and MAN1A2 were linearly and positively correlated with the hepatitis B e antigen (HBeAg) titer and HBV DNA level, although a positive correlation was only found between MAN1C1 expression and the HBeAg titer. These results indicate that increased -mannosidase I expression in PBMCs may play an important role in HBV immune escape and that its expression level is closely related to viral replication activity.