ObjectiveTo investigate the positive rate of class Ⅰintegron in Acinetobacter baumannii (AB) isolated from an intensive care unit (ICU),analyze the homology of multidrugresistant AB (MDRAB), and explore the molecular mechanisms of class I integron involved in drug resistance and the spread.MethodsForty MDRAB isolates from the ICU between January 2008 and December 2009 were collected, drug resistance of all isolates were detected by KirbyBauer method, PCR and DNA sequencing were undertaken to clarify the context of gene cassette. Pulsedfield gel electrophoresis was used to analyze the homology of MDRAB.ResultsClassⅠintegron was detected in 75.00% (30/40) of all isolates, 2 types of gene cassettes were identified, namely aacA4catB8aadA1 and aacC1orfXorfXorfX’aadA1. Forty isolates were classified into 4 distinct genotypes by PFGE analysis，26 isolates belonged to clone B that were predominant epidemic strain.Conclusionclass Ⅰintegrons are widespread in MDRAB, and spread horizontally in ICU. The epidemic of AB in ICU maybe caused by MDRAB carrying aacA4catB8aadA1 cassette.