The present study was conducted to evaluate the usefulness of four kinds of seaweeds (mixture of purple laver & sea lettuce, sea tangle, sea mustard, agar agar) as a high- fiber supplment in the therapeutic deit for the diabetic patients. Seven groups of normal and streptozotocin-induced diabetic rats were fed dietary fiber-free control diet or one of experimental diets containing 7% of one of the four seaweeds for 6 weeks. The effect of seaweeds supplementation on the body weight change, gastrointestinal function, and the control of diabetic symptoms were examined and compared with the effect of fiber-free diet or pectin diet used as references. The body weight gains of all the diabetic groups were significantly suppressed compared to the normal group. Feed efficiency ratios and body weight gains of seaweed groups were relatively higher than those of the pectin group. Sea tangle appeared to have an effect of alleviating the typical diabetic symptoms such as polyphasia, polydipsia, polyuria, urinary glucose excretion and hyperglycemia indicating its beneficial acition of improving glucose metabolism even though the degree of effectiveness was less than that with pectin. All the supplemntations of seaweeds and pectin ressulted in the significant changes in gastronitestinal functins ; shortening of GI transit time, increase of fecal volume and the length of intestine. Based on their effects of the significant changes in GI function in may be suggested that seaweeds may influence the process of digestion and absorption of nutrients in diabetic animals.