Aeromonas hydrophila is a Gram negative, positive oxidase, anaerobic, and opportunistic bacteria that, under certain conditions, become a pathogen (in humans and fish). This bacterium causes toxin and host infection in which different antibiotic resistance in isolated strains has been reported in different regions of the world. The aim of this study was to determine the prevalence of this bacterium and its susceptibility to common antibiotics in Tabriz city.50 samples from 5 Reared Oncorhynchus mykiss farms in Tabriz city (For each farm,10 numbers) were randomly assigned to suspected fish to the disease. By using biochemical tests, 14 samples (28%) from 2 Fish farms (40%) were identified as A.hydrophila. Antibiogram for these specimens showed that the bacterium had the highest resistance tovancomycin (100 %) and clindamycin (92.8%) antibiotics, and has the most sensitivity to the antibiotics ofsultrim, tetracycline and oxytetracycline with 71.4%.Considering the different antibiotic resistance pattern in this study and other similar studies,the necessity of examining the pattern of resistance in each region seems necessary.