〔Abstract〕 Objective To construct an Enterococcus faecium（Ef）-based recombinant Ef-PA0057 vaccine of Pseu⁃ domonas aeruginosa（Pa）and to study its protective immune mechanism in mice. Methods The PA0057 gene was cloned from the genomic DNA of PA01 strain ATCC9027 by PCR and inserted into pGEX-1λT to construct pGEX- PA0057. The recombinant plasmid was electroporated into TX0016 strain to construct rEf-PA0057 vaccine. The plasmid was extracted from rEf for PCR. The rEf vaccine was expressed through IPTG induction，and the expres⁃ sion of protein was analyzed by SDS-PAGE and Western blot. BALB/c mice were immunized intragastrically with 5× 108 CFU rEf-PA0057 vaccine 3 times per week for 3 weeks. 4 weeks after the first immunization，mice were chal⁃ lenged intranasally with 5× 107 CFU of PA01 strain. 2 weeks after challenge，mice were sacrificed，and their lungs were separated. Bacteria in lungs were incubated and colonies were counted. Sera were collected at 0，4，and 6 weeks after the first immunization. The IgG and its subclasses，and IgE were detected by ELISA. Results The 900 bp PA0057 gene was successfully cloned by PCR. PCR showed that PA0057 gene was amplified when the ex⁃ tracted plasmid from rEf as template；the relative molecular mass（Mr）of the expressed PA0057-GST fusion pro⁃ tein was approximately 58 ku，detected by SDS-PAGE. The amount of the expressed protein was 18% of the total bacterial proteins. Western blot showed that the target protein could be recognized by Pa sera. The colony numbers of lung tissue in rEf-PA0057 vaccine group，blank vector group and Ef control group were（0. 297±0. 011）× 108 CFU ，（7. 576±0. 206）× 108 CFU and（7. 551±0. 185）× 108 CFU ，respectively. The levels of IgG ，IgG1， IgG2b，IgG3 and IgE increased. At the same time point，there was a significant difference compared with the two control groups（P<0. 01）. Conclusion The rEf-PA0057 vaccine is successfully constructed. It may induce mice to produce a humoral response against challenge with Pseudomonas aeruginosa.