Abstract The antimicrobial activity and the composition of the essential oil of aerial parts of Nepeta rtanjensis DikliÄ et MilojeviÄ wild growing and cultivated in Serbia were evaluated. The main compound in both samples was characterized as 4aα,7α,7aβ-nepetalactone with 83.6% (wild) and 77.9% (cultivated). α-Copaene, germacrene D and δ-cadinene were present less than 5% in the oils. The antimicrobial activity of the oils was investigated by disk diffusion method. The oil-ethanol solution in three dilutions, tested against fve bacteria and a fungus, was effective towards all bacteria but not against Aspergillus niger. The oils showed bacteriostatic activity even in 1:60 dilution.