Fractions of a water insoluble α-(1→3)-D-glucan (GL) extracted from Ganoderma lucidum were carboxy-methylated (CM) to obtain water-soluble carboxymethylated derivatives (CM-GL) having a degree of substitution (DS) of0.38～0.51. Weight-average molecular weight M_w and intrinsic viscosity [η] of the samples CM-GL were measured by gelpermeation chromatography combined with laser light scattering (GPC-LLS) and viscometry. The CM-GL exhibits a stifferchain in aqueous solution at 25℃ than the original glucan, The antitumor activities against Ehrlich ascites carcinoma (EAC,5×10~6) of the carboxymethylated derivatives from the α-glucan and curdlan, a β-glucan, are significantly higher than thoseof the original glucans. The effects of the relatively low molecular weight, expanded chains and better water-solubility of theCM-GL on the enhancement of antitumor activity could not be neglected. The chain stiffness decreased speedily withincrease of temperature from 40 to 60℃ or NaOH concentration from 0.1 to 0.4 in the solution, respectively, and the changeof the chain stiffness is reversible. Fractions of a water insoluble α- (1 → 3) -D-glucan (GL) extracted from Ganoderma lucidum were carboxy-methylated (CM) to obtain water-soluble carboxymethylated derivatives (CM- of0.38 ~ 0.51. Weight-average molecular weight M_w and intrinsic viscosity [η] of the samples CM-GL were measured by gel permeation chromatography combined with laser light scattering (GPC-LLS) and viscometry. The CM-GL exhibits a stifferchain in aqueous solution at 25 ° C than the original glucan, The antitumor activities against Ehrlich ascites carcinoma (EAC, 5 × 10 -6) of the carboxymethylated derivatives from the α-glucan and curdlan, a β-glucan, are significantly higher than those of the original The effects of the relatively low molecular weight, expanded chains and better water-solubility of the CM-GL on the enhancement of antitumor activity could not be neglected. The chain stiffness decreased speedily withincrease of the temperature from 40 to 60 ° C. or NaOH conc. entration from 0.1 to 0.4 in the solution, respectively, and the changeof the chain stiffness is reversible.