The essential oil (yield 1.46%, w/w) of Monarda citriodora flowers obtained by hydrodistillation was analysed by GC-MS, Totally 30 constituents were detected. 26 compounds representing 97.23% were identified, of which thymol (44.599%), 1,8-cineole (23.613%), α-phellandrene (4.815%) and β-cymene (4.019%) were major compounds. Thus, the monoterpenes and sesquiterpenes were the predominant portions of the oil. Antibacterial ability of Monarda citriodora essential oil was tested by disc agar diffusion against Escherichia coli, Bacillus subtilis, and Staphylicoccus albus. Antibacterial properties were compared to penicillin. Higher antibacterial activity was observed.