Abstract: Objective To explore the effects of cefoperazone-sulbactam (C/S) plus minocycline on extensively drug resistant Acinetobacter baumannii (XDRAB) infections in critically ill patients.Methods For this prospective and single-center trial,a total of 101 patients with infection due to XDRAB received the primary therapy of C/S plus minocycline.Combined use of imipenem-cilastatin was considered when primary therapy failed.Results Among them,77 patients were evaluated.There were 49 males and 28 females with a mean age of (69 ± 20) years.The Acute Physiology and Chronic Health Evaluation (APACHE) Ⅱ score was 15 ± 5.Among whom 61 had hospital-acquired pneumonia (n =61),primary bacteremia (n =5),intra-abdominal infection (n =3),skin and soft tissue infection (SSTI) (n =2) and multiple sites infection (n =6).Twenty-three patients had mixed bacterial infections.Combined use of imipenemcilastatin therapy was administered in 7 patients.The treatment duration was (16 ± 4) days.The outcomes were cure (n =21),marked improvement (n =27),improvement (n =26) and ineffectiveness (n =3).The overall effective rate was 62.3% (48/77)and the microbiological clearance rate 46.8% (36/77).The independent factors of decreased efficacy were underlying co-morbidity of impaired ability for infection control (OR =5.3,P =0.020),prolonged infection (OR =3.8,P =0.029),co-infecting organism (OR =3.5,P =0.032) and septic shock (OR =2.5,P =0.037).Conclusions The combined regimen of C/S and minocycline is efficacious in the treatment of infections caused by XDRAB.But it has a lower rate of microbiological eradication.