Nosocomial infections caused by carbapenem-resistant Acinetobacter baumannii are increasing, and results mostly from the expression of acquired carbapenem-hydrolysing class D β-lactamases (CHDLs). This study aimed to evaluate the occurrence of bla (OXA-like) carbapenemase among clinical A. baumannii isolates. A total number of 140 non-duplicate A. baumannii with different origins were isolated from patients with proved nosocomial infections at two hospitals in Tehran and Shiraz city in Iran. Phenotypic and genotypic tests were used for bacterial identification. Antimicrobial susceptibility of these strains was checked by Kirby-Bauer disk diffusion test against ten antimicrobial agents. Minimal inhibitory concentration was measured by agar dilution according to CLSI guidelines. All of the 140 A. baumannii isolates harbored intrinsic bla OXA-51 gene. There was a high incidence of bla OXA-23 which may be associated with the high level of carbapenem resistance. Highest resistance was observed against imipenem (by agar disk diffusion) (92.0%) and lowest resistance was seen toward ampicillin-sulbactam (17.1%). All isolates were susceptible to colistin.