A genomic library of S. flexneri 5 large plasmid (140 Md) was constructed using the cosmid pJB8 as vector. There were more than 4,000 transformants in the library. 66 clones were picked out from the library by hybridization with 17kb gene probe relative to invasive ability. A few clones were analyzed. The results indicated that all these clones tested contained recombinant plasmids, they could hybridize with 17 kb gene probe. When these recombinant plasmids were digested with EcoR1, 17 kb fragments which hybridized with 17 kb gene probe always existed in these recombinant plasmids. It showed that all these recombinant plasmids contained the DNA fragments relative to invasive ability. It provides the possibility to construct an oral living vaccine against S. flexneri.