Schizophyllan, scleroglucan and lentinan, which are β-1, 3-glucans derived from Schizophyllum commune, Sclerotium glucanicum and Lentinus edodes, respectively, were evaluated for their ability to enhance protection to Edwardsiella tarda infection in carp Cyprinus carpio. Intraperitoneal injections of these polysaccharides (2-10mg/kg) to carp 6 and 3 days prior to intraperitoneal challenge with E. tarda (5×10⁷CFU/100g) resulted in a significantly increased survival rate. In all polysaccharide-treated groups, the rapid elimination of the challenge bacteria from the blood was observed and phagocytic activity of pronephros cells against baker's yeast was significantly elevated. Furthermore, it was shown that these polysaccharides activated the alternative complement pathway of carp. These results indicate that schizophyllan, scleroglucan and lentinan enhance the resistance of carp to bacterial infection through the activation of the non-specific immune system.