Aromatic and medicinal plants are widespread throughout world. Essential oils obtained from different aromatic and medicinal plants parts have been shown antibacterial, antifungal, antiviral and antioxidant properties. The experiment was started in season 2010-2011. In this study we studied the chemical compositions of essential oils of Lavandula officinalis and Melissa officinalis and also tested antibacterial and anticandidal activities of essential oils. The essential oils of Lavandula officinalis and Melissa officinalis collected in Iran were obtained by hydrodistillation of the aerial parts and analysed by gas chromatography equipped with flame ionisation detector (GC-FID) and gas chromatography coupled to a mass spectrometry system (GC/MS) for their chemical composition. The main constituents of leave oils were α-pinene, Camphor, Menthol, 1,8-Cineole, β-pinene, linalool, thymol and carvacrol. This experiment indicated that the bacterial strains were sensitive to studied essential oils and also showed very effective bactericidal activity with the strongest inhibition zone. Among the eight of tested essential oil components, thymol, carvacrol and menthol showed the highest antibacterial activities than previous components and streptomycin while, β-Pinene and linalool showed lower antibacterial activity than streptomycin (p = 0.05). Essential oils of Lavandula officinalis and Melissa officinalis possess great antibacterial potential and could be used as natural preservatives and fungicides.