The outbreak of diseases is a limiting factor in fish farms. A large number of plants are being used in traditional medicine for the treatment and control of diseases. One of such plants is ginger (Zingiber officinale). In this study antimicrobial effects of alcoholic extracts of ginger on six important positive and negative gram bacteria including Vibrio alginolyticus, Vibrio parahemolyticus, Micrococcus luteus, Staphylococcus epidermicus, Bacillus cereus, Stereptococcus zoo epidermicus were analyzed. Extraction was conducted on rhizomes of Ginger using 80% ethanol in laboratory. In order to assess antimicrobial effects of the ginger extract on the studied bacterial species, diffusion test on agar media using disk method on studied bacteria was conducted. Minimum Inhibitory Concentration (MIC) and Minimum Bactericidal Concentration (MBC) were determined by serial dilution assay using Liquid culture in 96 wells microplates. Results indicated that ginger alcoholic extracts have inhibitory effects on the bacterial growth and is lethal for all bacterial strains. Also ginger alcoholic extract has the most and the least growth inhibitory and lethal affects on Vibrio alginolyticus and Vibrio parahemolyticus, respectively.