A series of clinical isolates of drug-resistant (DR) Acinetobacter baumannii with diverse drug susceptibility was detected from eight patients in the emergency intensive care unit of Tokai University Hospital. The initial isolate was obtained in March 2010 (A. baumannii Tokai strain 1); subsequently, seven isolates were obtained from patients (A. baumannii Tokai strains 2-8) and one isolate was obtained from an air-fluidized bed used by five of the patients during the 3 months from August to November 2011. The isolates were classified into three types of antimicrobial drug resistance patterns (RRR, SRR and SSR) according to their susceptibility (S) or resistance (R) to imipenem, amikacin and ciprofloxacin, respectively. Genotyping of these isolates by multilocus sequence typing revealed one sequence type, ST208, whilst that by a DiversiLab analysis revealed two subtypes. All the isolates were positive for bla(OXA-51-like) and bla(OXA-66), as assessed by PCR and DNA sequencing. A. baumannii Tokai strains 1-8 and 10 (RRR, SRR and SSR) had quinolone resistance-associated mutations in gyrA/parC, as revealed by DNA sequencing. The ISAba / upstream of bla(OXA-51-like) and aminoglycoside resistance-associated gene, armA, were detected in A. baumannii Tokai strains 1-7 and 10 (RRR and SRR) as assessed by PCR. Among the genes encoding resistance nodulation division family pumps (adeB, adeG and adeJ) and outer-membrane porins (oprD and carO) overexpression of adeB and adeJ and suppression of oprD and car were seen in isolates of A. baumannii Tokai strain 2 (RRR), as assessed by realtime PCR. Thus, the molecular characterization of a series of isolates of DR A. baumannii revealed the outbreak of ST208 and diverse antimicrobial drug susceptibilities, which almost correlated with differential gene alterations responsible for each type of drug resistance.