Objective：To investigated the inhibitory effect of B7-2 on pulmonary metastasis by B7-2 gene transfection into breast cancer cells. Methods：A pair of PCR inter primers for B7-2 KpnⅠ was designed based on the sequence registered in GenBank. XbaⅠand KpnⅠ sites were introduced into the 5′ ends of the primers，respectively. Adequate parts out of each end of B7-2 gene in genome were taken as a pair of outer primers. Mononuclear cells were isolated from human peripheral blood，incubated until clustering. Reverse transcript total RNA that isolated from those clustering cells. B7-2 gene was amplified with outer and inner primers with PCR. The PCR fragments were digested with the above two enzymes and then cloned into pcDNA3.1（+） vector to construct recombinant plasmid called B7-2pcDNA. The correct sequencing B7-2pcDNA clone was amplified and transtected into MD-MBA-231 cells. Another group of MD-MBA-231 cells were transfected with idling pcDNA3.1（+）. Both transfected groups and the control group were marked with FITC anti-human B7-2 antibody and then detected by flow cytometric analysis. MD-MBA-231／B7, MD-MBA-231／PCDNA3.1, and MD-MBA-231 cells were inoculated into BALB／c mice respectively. The influence of B7-2 on the tumorous metastasis was also observed. Results：The B7-2 recombinant gene was constructed and its length was 952 bp. The B7-2 coding sequence within it was 100% homology with B7-2 homo gene previously registered in GenBank. The flow cytometric analysis shew that B7-2pcDNA group was 36.77% and 51.88% higher than pcDNA3.1（+） and control ones in B7-2 express rate，respectively. The tumor growth rate of MD-MBA-231／B7 xenograft was significantly slower than MD-MBA-231 xenograft in BALB／c mice. MD-MBA-231／B7 cells in orthotopic implantation developed significantly less pulmonary metastasis than MD-MBA-231／pcDNA3.1 and MD-MBA-231 cells. Histologic findings showed that leukocytes were intensively infiltrated in both the MD-MBA-231／B7-2 tumors and its metastatic lesions，however，were scarcely observed in the lesions associated with MD-MBA-231 and MD-MBA-231／pcDNA3.1 cells. Conclusion：B7-2 may play an important role in inhibiting lymph node metastasis by the mechanism of enhanced immunogenicity，and that B7-2 gene transduction might be effective against lymph node metastases of breast cancer.