The composition of the water-distilled essential oil of Achillea multifida (DC.) Boiss. (Compositae) was analysed by GC and GC/ MS. Fifty-eight compounds were identified representing 93.9% of the total oil. a-Thujone (60.9%), beta-thujone (9.1%), sabinene (4.1%) and camphor (3.7%) were characterised as the main constituents. The essential oil was tested for its antimicrobial activity using a micro-dilution assay resulting in the inhibition (MIC: 62.5 - 250 mug/ml) of human pathogenic bacteria and yeast.