P. aeruginosa is an opportunistic human pathogen causing life threatening infections in immunocompromised patients, severe nosocomial infections in hospital settings and chronic infections in cystic fibrosis patients. Following the colonization of the host, by producing several virulence factors (elastase, alkaline protease, pyocyanin, phospholipase, exotoxin A, etc.) the bacterium causes tissue damage and enters the blood stream thus disseminates in the host. A mechanism called Quorum Sensing( QS) responsible for the regulation of many virulence factors produced by P. aeruginosa which is triggered with a cell density dependent fashion and helps the bacteria to act as a quorum and to overcome the host defense mechanisms. Two QS systems have been described in details: las and rHl . Two N- acylhomoserine lacton signal molecules regulate gene expression of bacteria when they reach a density sufficient level. QS systems regulate expression of virulence factors including biofilm formation of P. aeruginosa. Due to high antimicrobial resistance rate to antimicrobials of this bacteria alternative therapaeutic approaches, especially related with QS systems have been searched. QS inhibitors which prevent virulence factor production of P. aeruginosa may prevent chronic colonization especially in cystic fibrosis patients and could be a novel strategy to control infections.