Activity-guided fractionations of leaf extracts from Laurus nobilis L. led to the isolation of a known sesquiterpene lactone, deacetyl laurenobiolide (1). Compound 1 showed antimicrobial activity against periopathic pathogens (Actinomyces viscosus, Porphyromonas gingivalis, Prevotella intermedia and Actinobacillus actinomycetemcomitans), opportunistic Gram-positive bacteria (Staphylococcus aureus and Streptococcus pyogenes) and fungi (Candida albicans, Cryptococcus neoformans and Aspergillus fumigatus). Furthermore, acetylation and cyclisation of deacetyl laurenobiolide (1) yielded laurenobiolide (2) and a new compound, (5S,6R,7S,8S,10R)-6,8-dihydroxyeudesma-4(15),11(13)-dien-12-oic acid 12,8-lactone (3), respectively. Compounds 2 and 3 also showed antimicrobial activities. All compounds 1-3 demonstrated growth inhibitory effects with minimum inhibitory concentrations ranging from 31 to 1000 µg mL(-1). This is the first report of compounds 1-3 showing antimicrobial activities.