Acinetobacter baumannii is one of the significant pathogens to cause healthcare–associated infection worldwide, mainly infecting critically ill patients. The present study aimed to analyse the antimicrobial resistance of Acinetobacter baumannii in a tertiary care hospital. Acinetobacter baumannii isolates were identified during one year period in a tertiary care hospital. Antimicrobial susceptibilities were determined for 238 isolates by Kirby–Bauer disk diffusion method and VITEK2–AST cards (Biomérieux, France) according to the Clinical and Laboratory Standards Institute (CLSI) guidelines. Majority of samples analysed were from inpatient (91.6%) and predominantly from tracheal aspirates. The isolates of Acinetobacter baumannii were most resistant to piperacillin (97.61%), ceftazidime (95.71%) and least resistant to colistin (3.26%). The drug of choice in multidrug–resistant strains of Acinetobacter spp. are carbapenems and 83.62% isolates of Acinetobacter baumannii were resistant to imipenem. There is a high incidence of resistant isolates of Acinetobacter baumannii to a majority of antimicrobial classes, including carbapenems. This study will guide the empirical therapy and suggest that surveillance of antimicrobial resistance of Acinetobacter baumannii is necessary.