Seeds from Leucaena leucocephala or commonly known as white leadtree are rich in galactomannan, a reserved polysaccharide composed of d-mannose and d-galactose residues. Galactomannan was isolated from the mature seeds of L. leucocephala using water extraction followed by precipitation with ethanol and purified using ion-exchange chromatography. Pure galactomannan was successfully isolated with a yield of 50.31% (w/w). It was chemically analyzed by UV, NMR, FT-IR, GPC, and HPLC. The polysaccharide was further hydrolyzed and derivatized with 3-methyl-1-phenyl-5-pyrazolone (PMP) for determination of its monosaccharide composition using a pre-column derivatization HPLC-UV technique. It consisted of d-mannose and d-galactose with mannose:galactose (M/G) ratio of 1.01. The molecular weight of the galactomannan was found to be 64 kDa. Galactomannan obtained from this present work is soluble in water. FT-IR analysis, H-1, and C-13 NMR of the galactomannan produced are similar to those reported in the literatures.