Centaurea damascena a member of Asteraceae family was investigated for its aerial part essential oil composition and antibacterial activities. A total of 35 components were characterized with the presence of oxygenated terpenes that represents more than 86 % of the total essential oil components. The composition was dominated by 11.45 % fokienol, 8.8 % thymol, 8.21 % α-terpineol, 7.24 % chrysanthemic acid, 7.13 % terpinen-4-ol and 6.59 % borneol with a high degree of polymorphism in the occurrence of these compounds as compared with the different species of Centaurea. The antibacterial activity was assessed by using the disc diffusion methods and the minimum inhibition concentrations (MIC) using microdilution method. The essential oils from Centaurea damascena possessed antibacterial activity against eight out of ten tested microorganisms at 5 μg/mL. While same oil showed only inhibitory activity at 20 μg/mL against Klebsiella pneumoniae (BL) and Pseudomonas aeruginosa (BL). The MIC of essential oils of C. damascena ranged from 15-1000 μg/mL. A synergetic effect against E. coli and K. pneumoniae was observed when 5 μg/mL oils were used with some of the ineffective antibiotics such as gentamicin for E. coli and vancomycin, ampicilin and chloramphenicol for K. pneumoniae. The activity of the antibiotic cefixime was increased by 26 % against K. pneumoniae after combination with the oil suggesting using it as potential adjuvant in the antibiotic treatment of pneumonia caused by K. pneumoniae and other ailments caused by oil-susceptible bacteria.