Abstract: Pathogens were isolated from 25 eels suffering from red fin disease in the culture ponds of five eel farms. The isolated pathogen was proved to be Aeromonas hydrophila. Eighty seven strains were tested against oxytetracyclin, chloamphenicol, trimthoprim-sulfamethoxazole (TMP/SMZ) and furazolidone respectively to determine the MIC. The results showed high degrees of resistance of the pathogen to the four antimicrobial agents tested. The aferage MIC, MIC50 and percentage of resistant strains for oxytetracyclin were 109.3μg/ml, 50μg/ml and 78.8% respecttively; those for chloamphenical were 123.2μg/ml, 63.0μg/ml and 90.7% respectively; those for TMP/SMZ were 720/3600μg/ml, 126/630μg/ml and 42.5% respectively: and those for furazolidone were 79.7μg/ml, 63.0μg/ml and 65.5% respectively. The average MIC for the four antimicrobiol agents were 109.3, 102.7 and 26.6 times respectively the MIC of the sensitive control strains.