Antimicrobial activity and chemical composition of Plectranthus aromaticus Roxb. essential oil from Grande Comore Island. This work aims to study the antibacterial and antifungal activity and chemical composition of Plectranthus aromaticus essential oil from Grande Comore Island. This species has provided an essential oil with a yield of 1.31%. The chromatographic analysis (GC and GC/MS) of the essence of P. aromaticus has identified about 32 constituents which are the most dominant: the trans-verbenol (23.11%), carvacrol (22.96%) and 1,4-cineol (14.50%). The antimicrobial activity of this oil has been studied with respect to seven microorganisms. The essential oil of P. aromaticus has proven antibacterial and antifungal activity at low concentrations.