The E2 subunit vaccine has been considered a promising alternative to an attenuated classical swine fever (CSF) vaccine. However, it fails to induce a good cellular immune response. Given that immunogenic adjuvants can regulate the cellular immunity to achieve a maximum efficacy against antigens, immunostimulatory effects of porcine IL-28B on the CSF virus (CSFV) E2 subunit vaccine were evaluated in the present study. We expressed recombinant proteins E2-IL28B, E2, and IL-28B using CHO-S mammalian cells as an antigen expression platform, and three types of CSFV E2 subunit vaccines based on antigens E2-IL28B, E2 + IL-28B, and E2 were prepared, respectively. We found that both E2-IL28B and E2 + IL-28B antigens exhibited superior immunogenicity with dramatically induced antibody titers and neutralizing antibody levels than the E2 alone. Moreover, E2-IL28B or E2 + IL-28B, instead of E2, boosted cellular immune responses via obviously increasing the percentages of CD3