Abstract: Objective: To characterize the outer membrane proteins in a Carbapenem resistant Acinetobacter junii(A.junii) clinical isolate and to speculate their roles involved in drug resistance.Methods: A multi-drug,including imipenem,resistant A.junii strain ZN3858 was recovered from the sputum of an acute exacerbation of chronic obstructive pulmonary disease in patient.Species identification was performed by the API 20NE and the combination of ARDRA and RAPD fingerprinting analysis.With the reference of A.junii ATCC 17908,the outer membrane proteins(OMPs) profile was analyzed by sodium dodecyl sulfate polyacrylamide gel electrophoresis(SDS-PAGE) and the quantitatively different expressed proteins were selected.Matrix assisted laser desorption/ionization time of flight mass spectrometry(MALDI-TOFMS) and PCR were employed to study the characters of the proteins concerned.Results: This carbapenem-resistant A.junii isolates ZN3858 had reduced expression of 35-,and 47-kDa outer-membrane proteins resembling oprD and oprF precursor respectively,which were OMPs associated with antibiotic resistance.Meanwhile,40 kDa outer membrane protein(omp40) was unexpectedly up-regulated,which highly resemble HMB-AB,an imipenem resistance OMP in imipenem resistant A.baumannii.The partial coding DNA sequence(CDS) of omp40 was obtained and the Genbank Accession Number assigned as AY626903.Conclusions: Outer membrane proteins may be involved in multi-drug resistance in A.junii.omp40 in A.junii is probably the counterpart of HMB-AB in A.baumannii,further research is necessary to elucidate its function in imipenem resistance.