Background The vaccination of mice with DNA encoding single candidate antigens has failed to induce significant protection against Schistosoma japonicum (S. japonicum) challenge infections In this study, we evaluated the feasibility of using a multivalent DNA vaccine which co expressed S japonicum integral membrane protein Sj23 and murine cytokine IL 12 to induce protective immune responses Methods The plasmid pVIVO2 IL12 Sj23, a eukaryotic expression vector expressing Sj23 and murine IL 12 simultaneously, was constructed, identified, and tested for expression in vitro Its ability to protect against S japonicum challenge infections was analyed according to worm reduction rate and egg reduction rate after vaccination of BALB/c mice The serum levels of specific IgG antibody were determined by enzyme linked immuno sorbent assay (ELISA) and Western blot analysis Using cultured spleen cells, IFN γ and IL 4 post stimulation were quantified by ELISA The phenotypes of splenocyte populations were analyzed by flow cytometry (FCM) Results The plasmid DNA pVIVO2 IL12 Sj23 was proven to express well in vitro by transient transfection of HEK 293 cells Immunization resulted in a worm reduction rate of 45 53% and egg reduction rate of 58 35% ELISA and Western blot analysis indicated that immunized mice generated specific IgG against Sj23 Spleen cells showed significant increases in IFN γ but decreases in IL 4 No significant differences in CD4 + and CD8 + subgroup ratios were observed after the challenges Conclusions The multivalent DNA vaccine pVIVO2 IL12 Sj23 is sufficient to elicit moderate but highly significant levels of protective immunity against challenge infections Cytokine IL 12, as a gene adjuvant, was able to enhance the Th1 responses and, hence, the protective immunity Background The vaccination of mice with DNA encoding single candidate antigens has failed to induce significant protection against Schistosoma japonicum (S. japonicum) challenge infections In this study, we estimated the feasibility of using a multivalent DNA vaccine which co-expressed S japonicum integral membrane protein Sj23 and murine cytokine IL 12 to induce protective immune responses The plasmid pVIVO2 IL12 Sj23, a eukaryotic expression vector expressing Sj23 and murine IL 12 simultaneously, was constructed, identified and tested for expression in vitro Its ability to protect against S japonicum challenge infections was analyzed by according to worm reduction rate and egg reduction rate after vaccination of BAL serum serum of IgG serum were determined by enzyme linked immuno sorbent assay (ELISA) and Western blot analysis using cultured spleen cells, IFN γ and IL 4 post stimulation were quantified by ELISA The phenotypes of splenocyte populations were analyzed by flow cytometry (FCM) Results The plasmid DNA pVIVO2 IL12 Sj23 was proven to express well in vitro by transient transfection of HEK 293 cells Immunization resulted in a worm reduction rate of 45 53% and egg reduction rate of 58 35% ELISA and Western blot analysis showed that immunized mice generated significant IgG in Sj23 Spleen cells showed significant increases in IFN [gamma] but decreases in IL4 No significant differences in CD4 + and CD8 + subgroup ratios were observed after the challenges Conclusions The multivalent DNA vaccine pVIVO2 IL12 Sj23 is sufficient to elicit moderate but highly significant levels of protective immunity against challenge infections Cytokine IL 12, as a gene adjuvant, was able to enhance the Th1 responses and, hence, the protective immunity