Structurally, egg white (EW) is composed of four distinct layers: outer thin white, thick white, inner thin white and chalaziferous layer (including chalaza cords). In addition, the thick white can be further separated into a gel and a liquid fraction by using ultracentrifugation. There were large differences in the amounts of various ovomucin complex forms between the EW layers, but more or less the order was about the same despite the ovomucin form. The three most ovomucin-rich fractions were: chalaziferous layer > gel fraction of thick EW layer > thick EW layer. Furthermore, each ovomucin fraction was also degraded by using enzymatic hydrolysis. Only three hydrolysed ovomucin fractions were found to contain hemagglutination inhibition activity against Newcastle disease virus, namely thick white, inner thin white and the gel fraction of thick white. Moreover, both thick EW and gel fraction ovomucin showed antiviral activity against avian influenza virus subtype H5. In addition, gel fraction ovomucin also inhibited avian influenza virus subtype H7. All three ovomucin hydrolysates having hemagglutination inhibition activity also contained the highest amount of sialic acid. Structural characterization of ovomucin revealed that it is composed of two subunits, alpha- and beta-ovomucins, as EW protein formerly called alpha 1-ovomucin seemed to be ovostatin. However, it seemed quite possible that ovostatin is associated within beta- and alpha-ovomucins. This interaction might even have some effect on the physical nature of various EW layers.