Abstract: This study aimed to investigate the effect of carvacrol on the morphology, cell membrane integrity and permeability of Gram- negative Escherichia coli ( ATCC 8735) and Gram- positive Staphylococcus aureus ( ATCC3101) .Most samples from both strains exposed to carvacrol showed higher UV absorptions, conductivity values, and β- galactosidase activities compared with the control group and displayed a rapid rise trend. Thereafter, the values stabilized at a relatively steady state. Transmission and scanning electron microscopy images of bacterial cells exposed to carvacrol showed marked ultrastructural changes after 6 ~ 8h of exposure. The results of the present study demonstrated that carvacrol was capable of leading to the loss of cell wall and cytoplasmic membrane integrity, causing marked changes in the membrane permeability and cell morphology of E.coli and S.aureus at minimum inhibitory concentration ( MIC 0.31 mg / mL) concentration.