Carbapenem-restant A. baumannii has been increasingly reported worldwide. The combination of antimicrobial agents is commonly used to treat A. baumonnii infections. The objective of this study was to investigate activities of antibiotic combination combination against multidrug--resistant A. baumonnii isolates and the association with resistance mechanisms. A total of 200 A. baumonnii isolated from patients during 2010-2015 were included in this study. The resistance rates to imipenem, meropenem, cefotaxime, ceftriaxone, ceftazidime, cefepime amikacin, gentamicin, ciprofloxacin and colistin were 86.5%, 87.5%, 87.5%, 87%, 85.5%, 91%, 78%, 80.5%, 85.5% and 1.5%, respectively. Colistin is the most active antimicrobial agent. The blaoxA-23, blavEB-1, aph3/ and armA were the most common antimicrobial resistance determinants in representative A. baumannii isolates for carbapenem, cephalosporin and aminoglycoside resistance, respectively. Only blaoxA-23 carbapenemase gene (100%) was detected in carbapenem-resistant A. baumanni isolates. Fluoroquinolone-resistance was mainly caused by amino acid substitutions at S83L in GyrA and S80L or S80Y in ParC. Five isolates were investigated for antibotic resistance island. All isolates carried AbaR4 with the blaoxA-23 carbapenemase gene in Tn2006. The in vitro activities of carbapenems in combination with amikacin, colistin or fosfomycin were determined in carbapeem-resistant A. baumannii isolates carring blaoXA-23 carbapenemase gene by checkerboard and time-kill methods. The results demonstrated that the most effective combination was imipenem with fosfomycin