Efficacies of eleven polysaccharides including Bar (glycan extracted from Barley), curdlan, Dex (dextran sulfate), inulin, krestin, laminaran, levan, PO (glycan extracted from Pleurotus ostreatus), scleroglucan, YG (yeast glucan), and zymosan, in the protection of tilapia, Tilapia aureus P., and grass carp, Ctenopharyngodon idellus, against bacterial infections in vivo were examined. Four glycans, namely, Bar, krestin, scleroglucan, and zymosan were observed to significantly increase the survival rates of tilapia (80, 60, 70, and 60%) and grass carp (60, 70, 90, and 60%) (p < 0.05) after injection with Aeromonas hydrophila. The abovementioned four glycans were also found to raise the survival rates of tilipia (70, 60, 80, and 50%) and grass carp (50, 50, 70, and 50%) (p < 0.05) significantly after infection with Edwardsiella tarda. Moreover, Bar, curdlan, krestin, scleroglucan, and zymosan were also found to significantly increase the number of NBT-positive staining cells (p < 0.05), which might indicate that to activate non-specific phagocytes in fish is one of the antibacterial mechanisms of polysaccharides.L'objet de la presente etude etait d'evaluer l'efficacite de douze polysaccharides [Bar (glycan extrait du Barley), curdlan, Dex (sulfate de dextran), inuline, krestine, laminaran, levan, PO (glycan extrait de Pleurotus ostreatus), scleroglucan, YG (yeast glucan) et zymosan] pour la protection des tilapia (Tilapia aureus P.) et grass carp (Ctenopharyngodon idellus) contre les infections bacteriennes in vivo. Les resultats recueillis apres injection de Aeromonas hydrophila ont revele que Bar, krestine, scleroglucan et zymosan avaient permis d'accroitre de facon significative les taux de survie (SRs) de tilapia (respectivement de 80, 60, 70 et 60%) et de grass carp (respectivement de 60, 70, 90 et 60%) (p < 0,05). Les resultats recueillis apres injection de Edwardsiella tarda ont revele que Bar, krestine, scleroglucan et zymosan avaient permis d'accroitre de facon significative les SRs de tilapia (respectivement de 50, 50, 70 et 50%) (p < 0,05). Les essais d'adherence/NBT suggerent que Bar, curdlan, krestine, scleroglucan et zymosan ont permis d'accroitre de facon significative le nombre de cellules marquees NBT-negatives (p < 0,05).