Pseudomonas aeruginosa is a ubiquitous opportunistic pathogen that is becoming an increasingly common cause of hospital infections. It is an increasing problem in health care because of the numerous virulence factors that allow the bacteria to penetreate into and through the host's tissue and its ability to avoid the immune system of the host. It has numerous effective mechanisms of antibotic resistance, which further complicates the treatment process. Pseudomonas aeruginosa is capable of producing biofilm, which is controlled by quorum sensing. Also, quorum sensing controls the movement of the bacteria in the form of swarming, antibiotic resistance, formation and excretion of various virulence factors, such as proteases that have the ability to break down the host's tissue and other secondary metabolites that further complicate the infection. Since the resistance to conventional antibiotic therapy is constantly increasing, the possibility of using essential oils separately or in combination with antibiotics may be considered. Essential oils have long been known for their antimicrobial properties and due to several mechanism of action towards bacteria, they are taken into consideration as good candidates for P. aeruginosa growth testing. This study examined the effects of Satureja montana L. essential oil and its main component thymol at a concentration of 0,5 mg/mL, separately and in combination with amynoglicoside tobramycin at subinhibitory concentrations of 0,5 μg/mL and 2 μg/mL on swarming motility and the proteolytic activity of P. aeruginosa strains ATCC 27853, BB1285 (rmtD+) PA14 and PAO1. Tobramycin showed an inhibitory effect on swarming and proteolytic activity of all strains except BB1285 (rmtD+) because of its high resistance to aminoglycosides. Satureja montana L. essential oil acted inhibitory to the proteolitic activity of strain PA14, but for the strain PAO1 it had no visible effect, while for strains ATCC 27853 and BB1285 (rmtD+) it stimulated the proteolytic activity. Thymol demonstrated inhibitory effect of higher intensity towards proteolytic activity of strains PA14 and PAO1, promotive effect for BB1285 (rmtD+) and no effect for strain ATCC27853. Satureja montana L. essential oil and thymol had an inhibitory effect on the swarming of strains ATCC 27853, PAO1 and PA14, but for the strain BB1285 (rmtD+) they showed no effect, with thymol showing inhibitory effect of higher intensity. Satureja montana L. essential oil and tobramycin in combination showed synergistic effect on reducing the proteolytic activity for strain ATCC 27853, PA14 and PAO1, but for strain BB1285 (rmtD+) they had no significant effect. The combination of thymol and tobramycin demonstrated the same effect, but of a higher intensity. Satureja montana L. essential oil and tobramycin in combination reduced the swarming of strains ATCC27853, PA14 and PAO1, while for strain BB1285 (rmtD+) they had no signicificant effect. Antagonistic effect of tobramycin and Satureja montana L. essential oil was shown on strains ATCC 27853, PAO1 and PA14. Effects of combination of thymol and tobramycin on swarming was the same as that of the combination of tobramycin and Satureja montana L., but of a higher intensity, which indicates that thymol is a component that has the most significant effect in Satureja montana L. The results of this study will hopefully contribute to further research of new possibilities in fighting Pseudomonas aeruginosa infections.