Chitosan is known to be one of the natural chelating agents. It is derived from chitin which is a cellu1ose- like biopolymer distributed widely in nature, especially in shellfish, insects, fungi, and yeast. There are two forms of chitosans, water solube and insoluble. The purpose of the present study is to investigate whether water soluble chitosan can be applied to reduce the bioabailability of radiostrontium in foods. We compared the effect of water soluble and insoluble chitosans on the absorption of ingested radiostrontium(85Sr). Three percent water soluble and insoluble chitosan solutions were given ora1ly, and immediately after 85SrCl2 (0.2 μCi) was administered to rats using a orogastric tube. In one group water solube chitosan solution was given for additional 4 days. And in control group no chitosan was given. Each group consisted of 6 rats. The whole-body retention of 85Sr, determined by in vivo counting method, was lower in water soluble chitosan group than that of water insoluble chitosan group and that of control. Urinary excrecion of 85Sr in chitosan-treated rats was higher than that of control. And 5 day ingested group of water soluble chitosan showed least whole retention of 85Sr. In conclusion water soluble chitosan was more effective in reducing bioavailability of ingested radiostrontium in the gastronintestinal tract than insoluble chitosan.