In this study, the effect of caffeic acid on growth and survival of Yersinia ruckeri was examined by exposing the pathogen to 0, 0.01, 0.05, 0.1, 0.5 and 1% concentrations of caffeic acid solution for 24 hours. The activity growth and survival of bacteria cells in exposed to each of 0.5 and 1% concentrations was found higher than that in controls and the differences were statistically significant (p<0.05). But, no differences were found in the survival of Y. ruckeri between the control and other experimental groups (P>0.05). The antibacterial effect of caffeic acid against Y. ruckeri was demonstrated. Further investigations are necessary to study the in vivo effect of the drug and validate the benefit of using caffeic acid in preventing infection in fish