To investigate the enhancement of immunological activity of CpG ODN by chitosan gene carrier in mice, the effect of lymphocyte proliferation was detected in mice by using MTT, the levels of IgG and cytokines (IL-2 and IL-12) in serum were measured by ELISA and peripheral blood T lymphocyte subsets CD4+, CD8+ were analyzed by flow cytometry. Our results showed that spleen lymphocytes isolated from the CS-CpG ODN group of mice showed the strongest proliferation (SI =1.551), and the levels of IgG, IL-2 and IL-12 in serum were higher than those of other groups. Compared with the immunization with CpG ODN, the immunization with CS-CpG ODN gene carrier was more efficient in up-regulating the percentage of CD4+ T cells and the ratio of CD4+/CD8+ of mice. It was concluded that CS gene carrier of CpG ODN was much more effective in improving immunity of CpG ODN in mice.