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Medicinal plants represent an inexhaustible source of traditional and effective remedies thanks to the various active ingredients they contain. Secondary metabolites present in plant extracts, such as essential oils (EO), have remarkable pharmacological properties, including antimicrobial effects. Here, the chemical composition and antimicrobial effects of four Moroccan medicinal plants, <i>Rosmarinus officinalis</i> L. (<i>R. officinalis</i>), <i>Mentha pulegium</i> L. (<i>M. pulegium</i>), <i>Salvia officinalis</i> L. (<i>S. officinalis</i>), and <i>Thymus zygis</i> subsp. <i>gracilis</i> (Boiss.) R. Morales (<i>T. zygis</i>), traditionally used in Morocco to treat microbial infections, were addressed. EO were extracted using the hydrodistillation method, and analyzed by gas chromatography coupled with mass spectrometry (GC/MS). EO yields were of 3.64 ± 0.12, 3.53 ± 0.06, 2.48 ± 0.06, and 2.34 ± 0.08%, respectively, for <i>M. pulegium</i>, <i>R. officinalis</i>, <i>S. officinalis</i>, and <i>T. zygis</i>. The main bioactive components present in these EO were piperitenone (32.9%) and pulegone (32.8%) for <i>M. pulegium</i>, 1,8-cineol (43.8%) and camphor (18.7%) for <i>R. officinalis</i>, 1,8-cineole (16.8%) and <i>trans</i>-thujone (15.9%) for <i>S. officinalis</i>, and thymol (36.4%), carvacrol (24.1%) and cymene (23.5%) for <i>T. zygis</i>. These EO showed, according to the results of their antimicrobial activities, good effectiveness against bacteria and fungi. Moreover, the <i>T. zygis</i> EO showed the most potent activity against all bacteria studied, while that of <i>R. officinalis</i>, <i>M. pulegium</i>, and <i>S. officinalis</i> showed moderate activity against the <i>Enterobacter cloacae</i> of <i>Streptococcus agalactiae</i> and <i>Escherichia coli</i>. The antifungal activity tests revealed a strong antifungal activity for the <i>T. zygis</i> EO and a moderate activity for the <i>S. officinalis</i> EO. On the other hand, the EO of <i>R. officinalis</i>, and <i>M. pulegium</i> were found to be inactive at the doses used against the selected strains. In conclusion, our results show that the medicinal plants studied contain biologically active molecules with antimicrobial effects. They can replace synthesized molecules, especially in the formulation of additives, and for therapeutic, cosmetic, and food-processing purposes.