The essential oils obtained by steam distillation ofOriganum compactumandO. majorana, which were grown in Morocco, were examined by gas chromatography to determine their major constituents. The major constitutents ofO. compactumwere carvacrol (49.52%), p-cymene (21.22%) and γ-terpinene (14.21%), while the major constituents of theO. majoranawere linalool (32.68%) and terpinen-4-ol (32.30%). The oils, dried whole plants, and aqueous extracts derived from the leaves were examined for their antimicrobial activities on molds, yeasts and bacteria. The Minimal Inhibitory Concentration (MIC) was determined in every case. A total inhibition (100%) was obtained with theO. compactumoil at the concentration of 4 ppm on all the microbial species, whileO. majoranaoil totally inhibited yeasts and lactic acid bacteria at a concentration of 5 ppm. Aqueous extracts of the two plants were less inhibitory than their essential oils. The entire plants were also inhibitory to some strains of yeasts, molds and bacteria, andO. compactumwas more inhibitory thanO. majorana.