The effects of fucoidan on the survival rate of mice treated with total body irradiation were examined. BALB/c mice were pretreated with various doses of fucoidan prior to total-body irradiation and were monitored for 30 days. A significant improvement of survival was observed by pretreatment with fucoidan at 100 mg/kg body weight. Using this optimal dosage, survival was examined by radiation dose reduction analysis and a dose reduction factor (DRF) of 1.20 was determined at 30 days post-irradiation. Mice pretreated with fucoidan also exhibited dose-dependent increases in the number of bone marrow cells and endogenous spleen cell colonies at day 9 post-irradiation. It is concluded that the increased survival of whole-body irradiated mice pretreated with fucoidan may be attributable to the radioprotective effects of fucoidan on hematopoietic cell viability, proliferation and/or mobility, possibly through antioxidation or antiinflammatory mechanisms. Copyright © 2008 John Wiley & Sons, Ltd.