Abstract: To explore the effect of the infection of Porcine Circovirus Type II (PCV2) on the humoral immune response to the pseudorabies virus (PRV) vaccine, the profile of the antibodies against the PRV vaccine in sera of the piglets infected experimentally with PCV2 were determined. The piglets were randomly divided into two groups. The piglets inoculated with PCV2 and vaccinated against PRV were served as the PCV2 group, and the piglets not inoculated with PCV2 but vaccinated against PRV were served as the control. All the piglets were vaccinated against the attenuated PRV vaccine at 14 days post inoculation (DPI) of the PCV2. The specific antibodies to the viruses in piglet sera were detected with indirect ELISA. By 14 DPI, all piglets in the PCV2 group had developed the viremia to PCV2. At 7 days post vaccination (DPV) against the PRV, the antibodies specific to the vaccine could be determined in most piglet sera, thereafter, the concentration of the vaccine antibodies increased gradually. At 14 DPV, the level of the vaccine antibodies in the control group piglets was significantly (P<0.05) higher than those in the PCV2 group. At 21 DPV, however, there were no significant differences in the vaccine antibodies level between the two groups. These data showed that the production of the antibodies specific to the PRV vaccine in the experimental PCV2-infected piglets was delayed, and indicated that the PCV2 infection played an inhibitory role on the humoral immune response to the PRV vaccine.