The complete S1 gene from mouse hepatitis virus (MHV) was amplified by RT-PCR and cloned into the pMD18-T vector. After confirmed by the restriction endonuclease analysis and PCR amplification, the positive clone of S1 gene was sequenced and then was transferred into eukaryotic expressing vector pVAXI. The recombinant plasmid pVAX1-S1 was transfected into COS-7 cells. The expressed S1 protein was successfully detected with indirect immunofluorescent assay. Finally, The recombinant plasmid pVAX1-S1 was transformed by electroporation into attenuated Salmonella typhimurium strain SL7207 and confirmed by PCR and Salmonella agglutination test. The recombinant was named as SL7207(pVAX1-S1). 6-week-old BALB/c mice were inoculated orally with SL7207 (pVAX1-S1) at dosage of 5 x 10 (8) CFU, 1 x 10(9) CFU and 2 x 10(9) CFU respectively. The immunized mice showed no clinic symptom. The results suggested that SL7207 (pVAX1-S1) was safe for mice after oral immunization at dosage of 2 x 10(9) CFU or below. BALB/c mice were immunized orally with SL7207 harboring recombinant plasmid at the dosage of 109 and boosted two weeks later with the same dose, for a total of three times. The recombinant Salmonella SL7207 ( pVAX1-S1 ) could induce significant humoral immune response in mice compared with the control (P < 0.05 or 0.01) at 2 w post-boosting and 2 w post-three immunization. The antibodies against MHV were also detected in small intestinal mucosal samples from immunized mice at 2 w post-three immunization. These results indicated that recombinant SL7207(pVAX1-S1) induced both systemic and local mucosal immunity.