Salmonella enterica serovar Enteritidis (Salmonella Enteritidis) is one of the most reported foodborne pathogen bacterium throughout the world that causes large outbreaks and may result in deaths. Phenolic acids, synthesized in almost all plants, are important for plant metabolism and protection of plants. They can be thought as promising antimicrobial agents against Salmonella Enteritidis. Outer membrane proteins are unique structures to Gram-negative bacteria including Salmonella genus and they are the first targets to environmental changes. This study showed the antimicrobial effect of 3-HPAA, cinnamic acid and o-coumaric acid on Salmonella Enteritidis in vitro. Scanning electron microscopy was used for showing the changes in bacterial shapes. Their effects on the outer membrane protein profile were investigated via proteomic approach. According to results of 96-well microtiter plate assay used for antimicrobial effect determination, among these phenolic acids, 3-HPAA showed 100% growth inhibition and other phenolics retarded the bacterial growth. 30 mM was found as minimum inhibitory concentration (MIC) of 3-HPAA at 24th hour of the experiment. SEM results demonstrated that 3-HPAA causes bacteria to have collapses on cell surface while cinnamic acid and o-coumaric acid cause cells to elongate abnormally. SDS PAGE of the OMPs of bacteria who were exposed to phenolic acids showed changes in amounts of proteins in some protein bands compared to control OMPs. 2-D PAGE results of OMPs of control bacteria via OMPs of 3-HPAA, cinnamic acid and o-coumaric acid treated bacteria, changes in sizes of spots were observed.