The inhibitory effect of IgY against Vibrio parahaemolyticus and Vibrio vulnificus responsible for seafood-borne diseases was investigated in this study. Water-soluble fractions (WSF) of protein containing IgYs were isolated from the egg yolk of hens initially immunized with formalin-inactivated V. parahaemolyticus or V. vulnificus. Protein, total and specific IgY contents of the WSF were determined. The inhibitory and protective effects of IgYs on the growth of V. parahaemolyticus and V. vulnificus were assayed in liquid medium and in mice. IgYs showed high affinity to their corresponding antigens with high titer from day 28 onwards. Protein contents and total IgY concentrations remained stable throughout the immunization period, whereas specific IgY concentrations increased steadily and reached a plateau at day 49. Specific IgY powder (150 mg/ml) significantly inhibited further multiplication of both V. parahaemolyticus and V. vulnificus in liquid medium as compared with the control IgY. The bacteria count in mice feces was lower in mice pretreated with specific IgYs than in those pretreated with PBS or control IgY. Higher survival of mice was observed in the experimental groups pretreated with either anti-V. parahaemolyticus (75% survival) or anti-V. vulnificus (87% survival) IgYs, compared with those in the control groups pretreated with PBS or nonspecific IgY. All mice in the control groups died within three days after bacteria inoculation; hence, the protective effect of specific IgYs against infection caused by V. parahaemolyticus and V. vulnificus was demonstrated.