ObjectiveTo investigate an outbreak of nosocomial infection(NI) with multidrugresistant(MDR) Acinetobacter baumannii (A.baumannii) in an intensive care unit (ICU). MethodsNine strains isolated from patients and 24 strains isolated from   ICU environment during NI outbreak with MDR A.baumannii were typed by repetitive extragenic palindromicpolymerase chain reaction (repPCR) and antimicrobial susceptibility  was tested by KirbyBauer method. ResultsNine strains isolated from patients were    divided into 4 genotypes by repPCR,  type E1 and E2 had 4 and 3 strains respectively, both type E3 and E4 had 1 strain. 24 strains of  A .baumannii  were  isolated from the environmental samples, 17 of which belonged to type E1. Antimicrobial sensitivity test results showed that all clinical isolates and 19  environmental isolates  were  multidrugresistant strains.ConclusionThe MDR A.baumannii outbreak in ICU   was caused by transmission of E1 and E2 genotype A.baumannii among patients， and environment was also contaminated.