Objective　To construct a eukaryotic expression system with pcDNA3-PfCSP/Hela for the Circumsporozoite protein (CSP) gene of Plasmodium falciparum (P. falciparum), to observe the immune responses in BALB/c mice induced by the expressed proteins. Methods　The recombinant plasmid pcDNA3-PfCSP was transformed into the Hela cell line. The expressed protein was isolated and analyzed by using SDS-PAGE and used for immunization of BALB/c mice by subcutaneous, intravenous, and intraperitoneal adminstration. Enzyme-linked immunosorbent assay(ELISA), Dot-ELISA, Western blot, T lymphocyte proliferation test, natural killer cell(NKC) activity assay, and CD4+ and CD8+ T cell detection were used for observation of humoral and cellular immune responses. Results　Immune sera strongly reacted with the expressed protein, antibody titer was up to 1∶6400 as detected by ELISA. Western blot analysis revealed a specific band at 38.3?Kda. When the spleen cells of normal and immunized BALB/c mice were specifically stimulated with expressed protein, the optical densities were 0.12±0.03 and 0.34±0.04, respectively. The latter were significantly higher than the former (P<0.01). We used the MTT colorimetric assay to measure NKC activity of mice spleen. The results showed that the NKC activity of immunized BALB/c mice was remarkably higher than that of the controls (P<0.05). CD4+ and CD8+ T cells were detected by using monoclonal antibody immunofluorescence methods. The results showed that the percentage of CD4+ and CD8+ T cells of immunized group were significantly higher than that of control group (P<0.05). Conclusions　The humoral and cell-mediated immune responses and elevated NKC activity to products made with a eukaryotic expression system could be specifically detected in BALB/c mice. These findings indicate that the expressed protein could enhance the immune function in mice.