The heavy incidence and severe or lethal damages of toxoplasmosis clearly indicate the need for the development of a more effective vaccine. In the present study, we constructed a multiantigenic DNA vaccine, eukaryotic plasmid pcDNA3.1-SAG1-ROP2, expressing surface protein SAG1 and rhoptry protein ROP2 of Toxoplasma gondii, and examined the expression ability of the DNA vaccine in HeLa cells by Western blot. Afterwards, we investigated the efficacy of pcDNA3.1-SAG1-ROP2 with or without co-administration of a plasmid encoding murine interleukin-12 (pIL-12) as a genetic adjuvant to protect Bagg albino/c mice against toxoplasmosis. After T. gondii RH strain challenge, mice immunized with pcDNA3.1-SAG1-ROP2 displayed significant high survival rates. Moreover, the protection was markedly enhanced by pIL-12 co-administration. The results of lymphocyte proliferation assay, cytokine, and antibody determinations show that mice immunized with pcDNA3.1-SAG1-ROP2 elicited stronger humoral and Th1-type cellular immune responses than those immunized with single-gene plasmids, empty plasmid, or phosphate-buffered saline. Furthermore, co-immunization with IL-12 genes resulted in a dramatic enhancement of these responses. Our study indicates that the introduction of multiantigenic DNA vaccine is more powerful and efficient than single-gene vaccine, and the co-delivery of pIL-12 further enhanced the potency of multiantigenic DNA vaccine.