In this study, the ompS gene, a major outer membrane protein gene of Legionella pneumophila, was obtained from the DNA of Legionella pneumophila by PCR. The gene was cloned into prokaryotic expressional plasmid pUC18 to construct recombinant plasmid. The recombinant plasmid was transformed into E. coli strain BL21. The identification was made by means of restriction enzyme analysis, polymerase chain reaction, DNA sequencing analysis, SDS--polyacrylamine gel electrophoresis analysis and Western blot. The results showed that the ompS gene of 914 bp was amplified from Legionella pneumophila DNA, the recombinant plasmid pLPompS was constructed and its expression in prokaryotic cell was detected successfully.