ObjectiveTo investigate the causes of an outbreak of healthcareassociated infection (HAI) with multidrug resistance Acinetobacter baumannii  (MDRAb) in an intensive care unit(ICU).MethodsBy combination of prospective and retrospective investigation, 10 ICU patients who were infected with MDRAb lower respiratory infection from January 25 to February 10, 2012 were performed epidemiological study.ResultsAb isolated from 10 patients’ sputum  were resistant to 16 antimicrobial agents except sensitive to cefoperazone/sulbactam  and intermediate sensitive to levofloxacin. Seven patients  were recovered after therapy,  3 died. A total of 104 environmental specimens (before cleaning) were taken,  Ab were isolated from 16 specimens such as faucet, treatment trolley, bedside table, nebulizer tube,  breathing tube, operation screen of  breathing machine, and hands of health care workers; Ab from 16 environmental specimens and patients’ sputum had the same antimicrobial resistance pattern. Outbreak was controlled after comprehensive measures were taken.ConclusionThe outbreak of MDRAb HAI  in  ICU is closely related to the contamination of  health care workers’  hands and hospital environment.