Abstract The essential oil of the aerial parts of Ammoides pusilla was analyzed using both GC and GC/MS. The results revealing no less than 46 constituents among which thymol (44.5%), Î³-terpinene (32.9%) and p-eymene (13.5%) were the most abundant. The antimicrobial activity of A. pusilla oil was studied using the agar diffusion test on eight strains of bacteria, and against fungus and yeast. The two-fold oil solution showed an important antimicrobial activity against Serratia marcescens, Salmonella enteritidis, Escherichia coli (ATCC 25922), Pseudomonas aeruginosa (ATCC 27853), Staphyhloccus aureus (ATCC 25923), Klebsiella pneumoniae, Pseudomonas syringae pv. syringae, Pseudomonas syringae pv. mosprunorum, Aspergillus niger and Candida albicans.