A rapid dissemination of carbapenem-resistant Acinetobacter spp. represents a significant clinical threat. Production of OXA carbapenemases and metallo-β- lactamases (MBLs) is the most important mechanism in acquiring carbapenem resistance in Acinetobacter spp. Carbapenem resistance has also ascribed to non- enzymatic mechanisms, including changes in outer membrane proteins, alterations in the affinity or expression of penicillin-binding proteins, and overexpression of efflux pumps. The most important mechanism in A. baumannii isolates from Korea is the production of OXA-23, while that in other species of Acinetobacter is the production of metallo-β-lactamases. (Korean J Clin Microbiol 2009;12:1-5)