In this study, chitosan-copper complexes were synthesized with different ratio in order to improve its antimicrobial activity. Native chitosan and chitosan-copper complexes (5% chitosan-Cu 2+ and 10% chitosan-Cu 2+ ) were evaluated their antimicrobial effects against Vibrio vulnificus and Vibrio anguillarum, which gave rise to the outbreak of fish disease in aquacultural farms. Three kinds of samples suppressed the growth inhibition depending on incubation times and concentrations, and the activity was increased with increasing concentration of copper ions. Thermal stability experiment revealed that native chitosan and chitosancopper complexes incubated at high temperatures showed excellent antimicrobial activity as compared to incubation at room temperature. The activity was also depending on inoculation times. These results indicate that chitosan-copper complexes would be used as antimicrobial agents against fish pathogenic bacteria such as vibrio species. Keywords : Chtiosan, Copper, Antimicrobial activity, Complex