Fifty farmed gilthead seabream and two water samples were collected from two semi-intensive marine farms at Damietta province, Egypt during 2016. Fourteen Vibrio alginolyticus isolates were recovered and presumptively identified using morpho - chemical characterization then definitely confirmed by PCR targeting species specific collagenase gene.The total prevalence of the examined fish was 28% (14/50). All strains were resistant to ampicillin, oxacillin, tobramycinand kanamycin. On the other hand, all strains were sensitive to levofloxacin, gatifloxacin, doxycycline, oxolinic acid, flumequine and trimethoprim/sulfamethoxazole. The LD50 of Vibrio alginolyticus isolate (VAS7) were 3 × 105 CFUg-1 of fish body weight.