Shrimp aquaculture has expanded rapidly in many countries and this rapid development resulted diseases outbreaks and further considerable utilization  of antibiotics. Use of natural products as antimicrobial has been reported as a resolution problem. The crude extract of a red seaweed (Laurencia snyderiae) collected from the Persian Gulf was evaluated for shrimp growth performance and to determine in vivo efficacy of this seaweed to prevention of  shrimp Vibriosis. The ethanol extract of Laurencia snyderiae was not toxic to the Artemia in star- I when it was fed to them for enrichment.  The white shrimp (Litopenaeus vannamei) Juveniles fed with these enriched Artemia at 0 mg mL-1 (Control group), and three treatments of 200 , 400   and 600 mg mL-1  for a 30 days period. Results showed an increase in survival rate in treatment groups compared with control group but wasn’t significantly (P<0.05). Shrimps that fed with enriched Artemia showed a significant in growth parameters compare ing to  Control group (P<0.05). The notably lower mortality was observed when these juvenile shrimps were challenged to Vibrio harveyi (after 30 days)  in comparison with  Control. The  results indicated that EELS has a good potential in growth- promoting and antibacterial activity against V. harveyi in which  is useful  in shrimp aquaculture.