Essential oils of  marjoram (Origanum majorana), rosemary (Rosmarinus officinalis), sage (Salvia officinalis) and thyme (Thymus vulgaris), were tested for their antimicrobial activity against  four Gram-negative bacteria, four  Gram-positive bacteria, four filamentous fungi and two yeast species which possess an importance as food spoilers or pathogenic microorganisms. The antimicrobial activity of tested essential oils at different concentrations (1,2,3,5 and 10 mg/ml) was determined by the well agar diffusion method. Sage and thyme essential oils showed the highest inhibitory effect against tested microorganisms, followed by rosemary and marjoram essential oils. The microbial spectra were decreased with increasing the concentrations of essential oils.