Genus Hypericum L. includes great number of herbal species, H. perforatum L. being the most significant and the most investigated one. There are less data about other species of this genus, although they can be interesting both from scientific and practical point of view.

We have therefore focused our attention to Hypericum olympicum from the area of southeast Serbia from which we have isolated essential oil and examined its chemical composition and antimicrobial properties.

The chemical composition of the essential oil was examined by GC-MS method under the following conditions: gas chromatograph Hewlett Packard 5890, mass detector Hewlett Packard 5971, Column SPB-5 (30 m, ID 0.25 mm, 0.25 mm film thickness), flow He 1 ml/min temperature regime: 50°C, 2 min., 5°C/min, up to 300°C and detector EMV 2800 V.

The obtained mass spectra were compared with corresponding base of the Wiley library. Forty components were detected and the most important 12 were identified.

We have applied dilution method on liquid nutritive media (Medium 3 - Defco I TSB-Torlak) with cellulose discs for investigation of antimicrobial action of the essential oil (MIC and MLC), by using the following 10 test cultures: Escherichia coli 95,Pseudomonas aeruginosa ATCC 9027, Staphylococcus aureus ATCC 6538, Klebsiella pneumoniae ATCC 10031, Salmonella enteritidis ATCC 13076, Sarcina lutea ATCC 9341, Bacillus subtilis ATCC 6633, Candida albicans ATCC 10231, Aspergillus niger ATCC 16404.

The essential oil shows the best antimicrobial action (MIC - 5 ml - MLC - 10m l) in the following test cultures: Pseudomonas aeruginosa ATCC, Staphylococcus aureus ATCC 6538, Salmonella enteritidis ATCC 13076, Bacillus subtilis ATCC 6633,Bacillus subtilis NCTC 8236 and the following test cultures are less sensitive: Klebsiiella pneumoniae, Sarcina lutea ATCC 9341.