The essential oil obtained by hydrodistillation from the leaves of Saudi Arabia native Mentha longifolia (Lamiaceae) was analyzed by gas chromatography-mass spectrometry GC/MS. Forty six compounds were analysed, it was characterized by a high percentage of oxygenated monoterpenes (30.40%) with Piperitone as the major one (30.77%), followed by sesquiterpen hydrocarbons (26.08%) in which Caryophellene (5.58%) as the main, while monoterpene hydrocarbons (23.90%) with gamma-Terpinene (1.36%) as a main. The principal components of M. longifolia oil was the piperitone with chemical formula C10H14O. The antibacterial activity of the essential oil of M. longifolia L. leaf were evaluated in this study. The essential oil showed strong antibacterial activity against Bacillus subtilis with inhibition zone (25mm) and Escherichia coli (24mm), It seems that the essential oils derived from the Mentha longifolia L. oil could be used as a natural source of antimicrobial agents.