Due to the high productivity L. leucocephala is important plant resource in tropical region. The leaves and the culm of L. leucocephala are widely used as feedstuffs and fertilizers because of their high protein and calcium contents but the seeds have not been used effectively. The effect of galactomannan extracted from the seeds of L. leucocephala on serum, liver cholesterol concentration and digestive organ were investigated. The results obtained as follows. Total serum cholesterol and total liver cholesterol concentrations were significantly lower in rats fed L. leucocephala seed galactomannan or guar gum than those fed the fiber free diet + cholesterol. Serum triglyceride, serum phospholipid, and serum high density lipoprotein (HDL) levels were not significantly different among them, but serum very low density lipoprotein (VLDL) + low-density lipoprotein (LDL) cholesterol was markedly decreased. Relative liver weight was significantly lower in rats fed the diets containing water-soluble polysaccharides. The length and weight of the small intestine plus the large intestine were higher in rats fed water-soluble polysaccharide. The length of the small intestine was larger in rats fed the diets containing polysaccharide, the diet containing 5% L. leucocephala seed galactomannan was the most effective.