This study was conducted to explore the synergetic effect of a novel plasmid containing a porcine IL-6 gene and CpG motifs on immunity of mice in order to develop an effective adjuvant to boost resistance against infection. The synthetic oligodeoxynucleotide containing 11 CpG motifs was inserted into the reconstructed VR1020 plasmid containing the pig IL-6 gene (VRPIL6), designated VRIL6C, and then encapsulated in chitosan nanoparticles (CNP) prepared by ionic cross linkage, designated VRIL6C-CNP. The 3-week old mice were injected, respectively, with VRIL6C-CNP, VRIL6-CNP, CpG-CNP and VR1020-CNP to detect the changes of immunity. At 28 days post inoculation, the mice were challenged with virulent hemolytic serotype 2 Streptococcus to test their resistance against infection. The results showed that there was a significant increase in immunoglobulins and interleukins in mice receiving VRIL6C-CNP compared with the control groups, as well as an increase in the lymphocytes and monocytes in the inoculated mice, so that the immunity was remarkably improved in the VRIL6C-CNP group. The challenge provoked stronger immunity and protection against infection in the VRIL6C-CNP group than in the control mice that manifested severe symptoms and lesions. This suggests that VRIL6C-CNP could remarkably enhance the nonspecific immunity of mice, and facilitate the development of an effective immunopotentiator to promote the resistance of the animals against infection.