The formylmethylated and aminoethylated derivatives of schizophyllan (SPG), a beta-(1-->6)-branched (1-->3)-beta-D-glucan from Schizophyllum commune Fries, were prepared through dimethoxyethylated SPG which was synthesized by the reaction of SPG with dimethylchloracetal under an alkaline condition. The degree of the substitution of formylmethyl groups in the formylmethylated derivative of SPG was estimated as approximately 0.19, and the locations of formylmethyl groups in the derivative were predominantly located at O-6 and/or O-4 positions in glucose residues. The molecular weights of these derivatives were similar to that of SPG, and the helical structure of the derivatives did not seem to be different. The antitumor activities of the formylmethylated and aminoethylated derivatives of SPG against subcutaneously implanted sarcoma 180 solid tumor in mice by intraperitoneal (i.p.) administration were increased more effectively than that of SPG at a dose of 10 mg/kg/d for 7 d starting from 7 d after transplantation of sarcoma 180. The activities inducing tumor regressing factor of the formylmethylated and aminoethylated derivatives were 1.5 to 2 times stronger than that of SPG at a dose of 100 mg/kg. Formylmethylated and aminoethylated derivatives of SPG as well as SPG itself retained the potentiating activity for the reticuloendothelial system. The productions of soluble cytotoxic factors secreted from murine macrophages by the administration of the formylmethylated and aminoethylated derivatives of SPG, which were probably superoxide anion and tumor necrosis factor as measured by the potency of the nitro blue tetrazolium reduction and the cytotoxic activity against L929 cells, respectively, appeared to be more efficient than that of SPG.