BACKGROUND: Increasing numbers of Acinetobacter spp. resistant to multiple drugs, including carbapenem, has been a serious problem. The aims of this study were to determine carbapenem resistance patterns and mechanisms, as well as to study the molecular epidemiology of Acinetobacter spp. METHODS: Clinical isolates of Acinetobacter spp. were collected from May to November in 2006. Antimicrobial susceptibility testing was performed using CLSI disk diffusion and agar dilution methods. Metallo-beta-lactamase- and OXA carbapenemase-producing isolates were detected by PCR. Carbapenem resistance and hydrolytic activities were compared according to OXA type and presence of ISAba1. Pulsed-field gel electrophoresis (PFGE) was performed to determine the epidemiologic features. RESULTS: The imipenem non-susceptible rates were variable from 10% to 67%. Among 151 isolates carrying bla(OXA-51-like), 75 isolates carried both bla(OXA-51-like) and ISAba1, and 25 isolates had both bla(OXA-51-like), bla(OXA-23-like), and ISAba1. Carbapenem MICs of both bla(OXA-51-like) and ISAba1-carrying isolates were higher than those with bla(OXA-51-like) only. Carbapenem MICs of bla(OXA-23-like)-carrying isolates were higher than those with both bla(OXA-51-like) and ISAba1. Both bla(OXA-51-like) and ISAba1-carrying isolates and blaOXA-51-like, blaOXA-23-like, and ISAba1-carrying isolates demonstrated higher hydrolysis activities in oxacillin and carbapenems. Most of the tested isolates were susceptible to tigecycline, and all of them were susceptible to colistin. Pulsed-field gel electrophoresis suggested that there had been several outbreaks of bla(OXA-23-like) and bla(OXA-51-like)-positive strains. CONCLUSION: Carbapenem non-susceptible Acinetobacter isolates and OXA carbapenemase-producing isolates were prevalent. Dissemination of bla(OXA)-harboring isolates may make it difficult to treat infections due to carbapenem-resistant Acinetobacter spp. Further surveillance studies are required to prevent the spread of carbapenem resistance.