Abstract: HOFARIGHUN, RAEE flower, thousand eyes wort are popular names for Hypericum sp in Persian language mostly called H. perforatum. It has been used as antispasmodic, diuretic, antimigraine, antiepileptic and cholagouge. Tisane of these plants in red wine was used as snake bite and burning remedy. The volatile constituents, obtained from air-dried aerial parts of fruiting Hypericum elongatum were analyzed by GC/MS method. Thirty four components of about 96.50% of total oil were identified. Pinene <α> (80.43%), Terpinene <γ> (4.23%) and Pinene <β>(2.59%) were the principal components (87.16%). The essential oil and hydroalcoholic extract were evaluated for antibacterial, antifungal and anti-yeast activities by using disc diffusion method. Screening of the antimicrobials was investigated on Gram positive bacteria (Staphylococcus aureus PTCC 1112, Staphylococcus epidermidis PTCC 1114, Bacillus subtilis PTCC 1023, Enterococcus faecalis ATCC 8043), Gram negative bacteria (Escherichia coli PTCC 1338, Pseudomonas aeruginosa PTCC 1047, Salmonella typhi PTCC 1609), yeasts (Candida albicans ATCC 14053, Candida kefyr ATCC 3826) and fungi (Aspergillus niger PLM 1140, Aspergillus fumigatus PLM 712). The MIC of essential oil also was identified. Antimicrobial activity of essential oil against all of the microorganisms was observed, except Aspergillus niger and Aspergillus fumigatus. In spite of antimicrobial activity of hydroalcoholic extract against bacteria, there was no antimicrobial activity against fungi and yeasts. A survey of the literature revealed no reports dealing with chemical composition of essential oil and antimicrobial activity of Hypericum elongatum.