Abstract: OBJECTIVE To investigate the distribution of resistant genes in a group of multidrug-resistant Acinetobacter baumannii isolated from the same ward, and their relationships among strains. METHODS A total of 25 strains of multidrug-resistant A. baumannii were collected from sputums in the same ward from Jan. 2014 to Dec. 2014. Species gene of A. Baumannii were identified by PCR, then, resistance genes were analyzed by PCR, including 11 kinds of beta-lactamase genes, 3 kinds of linkage detection of beta-lactamase genes and insertion sequences, 9 kinds of resistant genes to aminoglycosides, one kind of resistant gene to quinolones, 2 kinds of genetic markers of mobile genetic elements. In addition, sample cluster analysis was performed. RESULTS Resistant genes to beta-lactams, aminoglycosides, genetic mutation of target position gyrA in quinolones were all positive in every of the 25 strains. Furthermore, 3 kinds of beta-lactam-resistance genes (blaTEM , blaSHV, blaADC), 6 kinds of aminoglycoside-resistance genes (armA , aac(3)-Ⅰ, aac(3)-Ⅱ,aac(6')-Ⅰb, ant(3″)-Ⅰ, ant(2″)-Ⅰ) were positive, mutations existed in all gyrA, 2 kinds of genetic markers of mobile genetic elements(intⅠ1, ISaba1). Linkage detection of beta-lactamase gene and insertion sequence showed that positive rates of blaADC and ISaba1 were 100%. Sample cluster analysis showed that 5 clones existed in this group, 25 strains were divided into two clusters: A and B. Cluster A were divided into A-1 and A-2. Strain No.1-2-9-10-11 in cluster A-1, and strain No. 3-6-7-14 and 15-17 in A-2 were cloned and propagated. Cluster B were divided into B-1 and B-2. Strain No.5-13-16-19-22-23-24 and strain No.20-21 were also cloned and propagated. CONCLUSION Agrreegation in this group of multidrug-resistant A. baumannii were obvious and 5 clones suggested that nosocomial infection existed. So it's important to real-time monitor and control noscomial infection depending on sample cluster analysis by negative and positive binary results of resistance genes to explain the relationship between resistance genes.