Abstract: With the rapid development and application of nuclear technology in China, the treatment to the potential danger of nuclear radiation has become a hot topic in the fields of medicine, health and society. In this study, we tried to investigate the protective effect of oligomeric chitosan and fucoidan on radiation-induced damage in the male Kunming mice. The mice were randomly divided into 6 groups: normal control group, irradiation control group, oligomeric chitosan low dose group (0.9 mg kg^-1 BW d^-1), oligomeric chitosan high dose group (3 mg kg^-1 BW d^-1), fucoidan low dose group (0.9 mg kg^-1 BW d^-1) and fucoidan high dose group (3 mg kg^-1 BW d^-1). They were given polysaccharides by gavage for 25 days except the mice in normal control group and irradiation control group were given deionized water in the same way. On the 17^th day, the mice in all groups except normal control group were irradiated with 4 Gy ⁶⁰Co γ ray. Immune index, genetic index and antioxidant activity were detected at the 1^th and 7^th day after radiation. The results showed that the thymus index and the spleen index of mice given oligomeric chitosan and fucoidan increased significantly, but no obvious dose-effect relationship was observed. It suggested that the two polysaccharides might have a protective effect on organ damage in irradiated mice. The amount of bone marrow DNA in the femur increased significantly in the groups of polysaccharide, especially the group of high dosage of oligomeric chitosan, indicating that the two kinds of polysaccharides can reduce the genetic damage induced by radiation. The content of GSH increased significantly, and the MDA content reduced significantly of the heart, liver, and kidneys in the groups of polysaccharide, which indicated that the two kinds of polysaccharides had significant antioxidant effects. The results suggested that oligomeric chitosan and fucoidan had protective effects on damage in γ ray irradiated mice. The possibility for the development of health care products in the future needs to be further explored.

Key words: oligomeric chitosan, fucoidan, Kunming mice, radiation damage, protection