Pseudomonas aeruginosa, which is an important oppurtunistic pathogen, is a serious threat for human health, worldwide. New antimicrobial agents are in search and phenolic acids, secondary metabolites of plants, are promising candidates. In this project, the protein profile changes of Pseudomoas aeruginosa were determined after phenolic acid exposure by shot-gun proteomics. It was aimed to enlighten the antimicrobial action mechanism of subinhibitory concentrations of phenolic acids on pathogenic bacteria via proteomic approach.