Abstract: Antibiotic susceptibility tests were carried out by K-B diffusion method on 41 vibrio strains isolated for one year both from farming seawater (18 strains) and digestion guts (23 strains) of the cobia, Rachycentron canadum. We chose 10 different species of antibiotics and refered to NCCLS performance standards for antimicrobial susceptibility testing, while taking Staphylococcus aureus ATCC25923 and Esсheriсhia coli ATCC25922 to control the test. Results showed that the most effective antibiotic for inhibiting growth of vibrio strains were Chloramphenicol (percentage of sensitive strains was 100%) and Gentamicin (percentage of sensitive strains from water and intestine was 100% and 90% respectively), followed byNorfloxacin, Compound Sulfamethoxazole Polymyxin B. It also showed that Penicillin G and Ampicillin were non-effective to majority of vibrio strains in the intestine, as 78% and 60% strains resisted to Penicillin G and Ampicillin respectively. Strains from farming water and intestine of cobia showed different sensitivity to the same antibiotic. 4 strains which resisted to 3 or more than 3 species antibiotics were sieved from this study.