Phenolic acids are known for their potential antimicrobial action, however their mechanisms of action are still unraveled. In this study, effect of phenolic acid stress on Listeria monocytogenes, a dangerous foodborne pathogen, was studied with a proteomic approach. Two phenolic acids found in olive oil, namely o-coumaric acid and ferulic acid, were applied on this bacterium via microtiter plate assay. The concentrations of these phenolic acids that inhibit the bacterial growth by 50% were determined as 7.5 mM for o-coumaric acid, and 8 mM for ferulic acid. Besides, minimum bactericidal concentration of o-coumaric acid was also found as 12 mM. Cellular proteomes of phenolic acid-treated and untreated bacteria were analysed with nanoLC-ESI-MS/MS system, and identified with MaxQuant/Andromeda bioinformatic toolbox. According to the results, both phenolic acids induced oxidative stress in L. monocytogenes cells. In addition to this, DNA replication and repair enzymes, nutrient uptake proteins and several proteins directly related with the virulence of L. monocytogenes were among the targets of phenolic acid stress. Last but not least, proteins associated with biosynthetic pathways were found to be predominantly downregulated. Moreover, the morphology of phenolic acid-treated and untreated cells was visualized with scanning electron microscope to support these findings. The images showed that lengths of treated cells were either abnormally elongated or shortened when compared to untreated cells. A possible reason for these abnormalities is the unequal fission promoted by two factors; excessive production of cell envelope biosynthesis and fission regulatory proteins, and repression of aforementioned DNA replication and repair enzymes.