ObjectiveTo investigate an outbreak of nosocomial infection(NI) with multidrugresistant(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 palindromicpolymerase chain reaction (repPCR) and antimicrobial susceptibility was tested by KirbyBauer method. ResultsNine strains isolated from patients were divided into 4 genotypes by repPCR, 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 multidrugresistant 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.