Pseudomonas aeruginosa is an opportunistic pathogen that most commonly leads to infections of immunocompromised individuals. It is considered to be the most clinically significant species within the genus Pseudomonas. The ability to produce a large number of structural and secretory virulence factors and to form biofilm complicates the treatment of P. aeruginosa infections. There is a great need to explore alternative treatment options because of the increase in development of bacterial resistance in P. aeruginosa, due to the irrational use of antibiotics. One of these alternative options is the use of essential oils. These are aromatic, volatile solutions of complex composition that possess antimicrobial activity. This study investigated the effect of Micromeria thymifolia (Scop.) Fritsch essential oil and its component pulegon in concentrations of 0,5 mg/mL on planktonic cell growth and production of virulence factor pyocyanin in P. aeruginosa PAO1. In addition to their individual effect, a potential synergistic effect with the aminoglycoside antibiotic tobramycin in subinhibitory concentration of 0,5 mg/L was also investigated. The effect on the planktonic growth of P. aeruginosa PAO1 cells was measured spectrophotometrically at 600 nm. Micromeria essential oil and pulegon used in concentration of 0,5 mg/mL showed an inhibitory effect on planktonic cell growth. Micromeria essential oil also showed a synergistic effect with tobramycin by enhancing its effect on growth of P. aeruginosa PAO1 plankton cells. The combination of pulegone and tobramycin did not lead to significant synergism. The effect on production of pyocyanin by P. aeruginosa PAO1 was investigated by spectrophotometric measurements of extracted pyocyanin at 520 nm. Micromeria essential oil showed an inhibitory effect, while pulegon did not. Interaction of tobramycin with essential oil and pulegon showed their antagonistic effect leading to a decrease in the activity of tobramycin. The results of this work contribute to a better understanding of the complexity and antimicrobial potential of essential oils.