Nature is an unexplored reservoir of novel phytopharmaceuticals. Since biofilm-related oral diseases often correlate with antibiotic resistance, plant-derived antimicrobial agents could enhance existing treatment options. Therefore, the rationale of the present report was to examine the antimicrobial impact of Mediterranean natural extracts on oral microorganisms. Five different extracts from Olea europaea, mastic gum, and Inula viscosa were tested against ten bacteria and one Candida albicans strain. The extraction protocols were conducted according to established experimental procedures. Two antimicrobial assays--the minimum inhibitory concentration (MIC) assay and the minimum bactericidal concentration (MBC) assay--were applied. The screened extracts were found to be active against each of the tested microorganisms. O. europaea presented MIC and MBC ranges of 0.07-10.00 mg mL(-1) and 0.60-10.00 mg mL(-1), respectively. The mean MBC values for mastic gum and I. viscosa were 0.07-10.00 mg mL(-1) and 0.15-10.00 mg mL(-1), respectively. Extracts were less effective against C. albicans and exerted bactericidal effects at a concentration range of 0.07-5.00 mg mL(-1) on strict anaerobic bacteria (Porphyromonas gingivalis, Prevotella intermedia, Fusobacterium nucleatum, and Parvimonas micra). Ethyl acetate I. viscosa extract and total mastic extract showed considerable antimicrobial activity against oral microorganisms and could therefore be considered as alternative natural anti-infectious agents.