Background and Objectives: Melissa officinalis belongs to plant Lamiaceae family and is native to Iran as well as other countries. The aim of this study was to identify chemical compositions and antioxidant activity of the M. officinalis essential oil -EO-. Another aim of this paper was to assess antimicrobial activity of M. officinalis EO on growth of clinical and commercial strains causing infection. Materials and Methods: Chemical compositions of the M. officinalis EO were analyzed using gas chromatography-mass spectrometry -GC-MS-. The antioxidant potential was assessed using β-carotene/linoleic acid inhibition and 2,2-diphenyl-1-picrylhydrazyl methods. The total phenol content was analyzed using Folin-Ciocalteu method. Antimicrobial activities of the M. officinalis EO were assessed using disk diffusion agar, well diffusion agar, micro-well dilution, agar dilution and minimum bactericidal concentration -MBC- methods. Results: Major compositions of the M. officinalis EO included geranyl acetate -27.9 %-, citral -14.2%-, Z-citral -9.8%- citronellal -8.4%- and citronellol -7.6%-. The total phenolic content and antioxidant potential of the M. officinalis EO included 51 ±0.50 mg GAE/g and 98 ±0.45 µg/ml, respectively. Minimum inhibitory concentration -MIC- of the M. officinalis EO ranged 0.5–4 mg/ml, while the MBC ranged 1–8 mg/ml. A significant correlation was seen between the inhibition zone diameters -IZD- and concentration of the EO. The smallest IZD was reported for various concentrations of the M. officinalis EO on Pseudomonas aeruginosa. Conclusions: In general, results showed that the M. officinalis EO included greater inhibitory effects on commercial bacterial strains causing infections, compared to those of clinical bacterial strains. The M. officinalis EO have the greatest effect on gram-positive bacteria. This compound is an effective free radical scavenger rich in phenolic compounds. Further studies are necessary to investigate toxicity of the M. officinalis EO due to its safety for human use.

Keywords