Oligobeta-glucan and oligochitosan were prepared by gamma Co-60 irradiation of Beta-glucan/H2O2 and chitosan/H2O2 solution. The efficiency of the degradation process was determined by gel permeation chromatography (GPC) method. Results showed that the Mw decreased with increasing concentration of H2O2 and doses. For oligobeta-glucan, Mw reduced from 56.7 kDa to 7.1 kDa when beta-glucan 10 percent/H2O2 1 percent solution was irradiated at 14 kGy. For oligochitosan, Mw reduced from 45.5 kDa to 5.0 kDa when chitosan 4 percent/H2O2 0.5 percent solution was irradiated at 21 kGy. Tra catfish (Pangasianodon hypophthalmus) was fed with oligopglucan and oligochitosan in various concentrations of 0, 50, 100, and 200 mg/kg feed for 45 days and then was challenged with Edwardsiella ictaluri bacteria to investigate immune stimulation effect against white patches in the internal organs disease. The "results indicated that oligopglucan and oligochitosan exhibited good immune stimulation effect with optimum concentration of 100 mg/kg feed.