This study was carried out to the determine antibacterial activities and chemical compositions of the essential oil of aerial part of Hyssopus officinalis obtained from the hydro – distillation. The chemical composition of essential oil was determined using gas chromatography/mass spectrometry (GC/ MS). Thirty nine components were identified in H. officinalis oil that thymol (18.95%), ß-bisabolol (10.62%), carvacrol (7.73%), n–Dodecan (5.23%), caryophyllene (4.96%), ortho – acetanisol (4.72%), camphor (3.47%), cumin aldehyde (3.22%) and spathulenol (3.02 %) as major components in essential oil. Antibacterial activity of the essential oil was evaluated the micro broth dilution and disc diffusion methods. The oil showed high antibacterial activity against Erwinia amylovora and Klebsiella sp. But on the other bacteria tested is ineffective.