Alkali soluble(AS) fraction, revealed the highest antitumor activity of the alkali extracted fractions of G. lucidum IY 009, was loaded on DEAE cellulose(OH$^{-}$ form) column. AS-1, AS-2, AS-3, AS-4 and AS-5 were obtained by stepwise elution with H$_{2}$O, 0.1 M NaHCO$_{3}$, 0.3 M NaHCO$_{3}$, 0.5 M NaHCO$_{3}$ and 0.5 N NaOH respectively, and their antitumor activities(I.R. %) against the sarcoma 180 were 97.5%, 68.0%, 73.0%, 81.0% and 66.0% respectively. AS-1 observed highest antitumor activity was appeared as single peak on the Sepharose CL-4B column chromatography, and their molecular weight was about 580,000 dalton. The carbohydrate content of AS-1 was 98.9%, their monosaccharide consisted of 67.5% of mannose, 22.5% of xylose, 5.8% of glucose, 1.8% of galactose and 2.0% of ribose. AS-1 was assumed $\alpha $linkaged xylomannan having infrared absorption at 864.3 cm$^{-1}$. The main alditol acetates of AS-1 were identified as 1,5-Di-O-acetyl1-2,3,4-Tri-O-methylxylitol, 1,4,5-Tro-O-acety1-2,3,6-Tri-O-methylmannitol and 1,3,4,5-Tetra-O-acety1-2,6-Di-O-methylmannitol by methylation analysis, and their molar ratio was 1 : 2 : 1. The core portion of AS-1 might be $\alpha $-(1$\longrightarrow $ 4)mannopyranosyl unit branched with side chain, C1 of xylopyranosyl residue linked to C3 of every 3 mannopyranosyl units, and the degree of polymerization of structural unit in AS-1 was about 835.